Encyclopædia Britannica, Ninth Edition/Gunmaking

by Eardley Maitland

UNDER this head falls the manufacture of every description of firearm, from the pistol to the 100-ton gun. The term " small arms " includes sporting and military weapons carried by the shooter ; instruments fitted for firing a rapid succession of bullets through one or more barrels from a rest are termed "machine guns;" while the heavier pieces, used exclusively in war, are denominated " ordnance."

Small Arms.

The date and circumstances of the introduction of portable firearms are involved in obscurity. No doubt many

attempts were made and failed previously, but gunpowder does not appear to have come into practical use as a rival to the crossbow for the propulsion of bolts or bullets till the reign of Edward III.; in 1375 mention is made of men armed with " gonnes " at an attack made on a Yorkshire manor-house. The arquebuse a meche was employed in Germany in 1378, and it is therefore probable that some rough weapon was introduced much earlier. The hand-gun (fig. 1) was used by both infantry and cavalry; it consisted of a simple iron or brass tube with touch-hole at the top, fixed on a straight stock of wood ; when used on foot, the soldier held it firmly by passing the stock under the arm; when used on horseback the stock was shortened to butt against the breast, the barrel resting on a fork secured to the saddle bow. About the beginning of the reign of Henry VII. the hand-gun was improved by the addition of a cock, which was brought down by a trigger to a pan at the side of the barrel; this cock held a match which ignited a priming in the pan, the priming communicating with the charge by a small hole. The next alteration consisted in the introduction of the wheel-lock, in which a steel wheel, rasped at the edge, protruded into the priming pan. Into the cock was fitted a piece of sulphuret of iron (pyrites) instead of a match; this was kept down to the priming pan by a spring; another spring, when wound up, acted on the SMALL AKMS.] GUNMAKING wheel, which, when released by the trigger, spun round, rubbing against the pyrites and causing sparks, which set fire to the priming. The wheel-lock was, however, found to be complicated, expensive, and uncertain, so that the match-lock remained in use till the middle of the 17th century, when it was displaced by the flint-lock, the earliest form of which, the " snaphaunce," seems to have been invented about the end of the 16th century in Germany. Tn this lock the priming pan was provided with a steel cover and the cock held a flint; on pulling the trigger the cock fell, the flint struck the steel cover, forcing it back from the pan, evolving at the same time sparks, which fired the priming. During these developments of the lock the shape of the barrel was gradually changed; in 1621 the length of that of the musket was 4 feet, and the size of the bore such that twelve bullets weighed 1 fib. Soon after this the infantry soldier was supplied with a dagger. FiQ. 1. Haud-Gun. which fitted into the muzzle and served as a pike. This was improved at Bayonne into the bayonet, and during the latter part of the 17th century was still farther improved by the addition of a socket, so that the musket could be fired while the bayonet was fixed ready for use. Little change in firearms took place in the 18th century, but in 1807 a Scotch clergyman named Forsyth obtained a patent for priming with fulminating powder, an invention which, though it slumbered till 1834, was destined to cause a complete revolution in the mechanism of firearms. Early in the present reign its value was fully recognized ; the magazine of detonating composition and the priming pan used by Mr Forsyth were improved into the cap and nipple, and the flint-lock was entirely superseded. At this point, the progress of invention renders it necessary for us to treat separately the two branches of the subject, and to divide sporting from military arms. For sporting purposes smooth-bored shot-guns and grooved rifles are employed. Both are nearly always double- barrelled, and of late years the old muzzle-loaders have been almost entirely supplanted by the many breech-loading systems recently invented, which enable the sportsman to reload with greatly increased rapidity and uniformity, the latter quality being specially important in rifle shooting. The chief parts composing the arm are the barrel, the lock, and the stock. Barrels for sporting arms are made of four different kinds of material Damascus twist, laminated steel, stub iron, and mild cast-steel; besides these, common material is worked up into cheap barrels for exportation. Damascus twist consists of alternate rods of iron and steel placed one upon another ; usually six of each kind are thus arranged ; they are then forged and thoroughly welded to gether into a solid bar, which is afterwards rolled into rods, having a section about f inch square. The rod thus formed is raised to a brightish red heat, and one end of it is placed in a revolving chuck, while the other remains fixed ; the turning of the chuck subjects the rod to a severe twisting throughout its whole length, so that at last -it acquires the appearance of a screw having a very fine thread. Three of these rods are then placed together, the twist of one being in a contrary direction to that of the other two. They are then welded together into a bar, and rolled into a strip about f inch in width. The thickness of this strip depends on the part of the barrel it is intended to form ; if for the breech end it is made ^ inch thick, if for the centre y inch, if for the muzzle |- inch. These strips are now ready for coiling, which is performed by raising the strip to a bright red heat, fixing one end of it to a hook projecting from a taper mandril, which is placed in a machine and provided with a handle. On turning the handle the strip is wound round the mandril into a coil about 10 inches in length. The coil is then welded by about 3 inches at a time till the spirals unite to form a hollow cylinder ; it is then hammered on a small mandril till the welding is complete. Three coils welded together end to end form a barrel, to which the three different thicknesses of metal above m entioned give a slightly conical form, approximating to the ultimate shape. About three- fourths of the material is cut away in the making; 16 tt> of iron are used in the first instance to make a pair of barrels, which weigh only 8 Bb when the welding is finished, and only between 3 and 4 ft) after boring and grinding, In the manufacture of laminated steel barrels the best quality of steel scrap, after thorough cleaning in a revolv ing drum, is mixed with a small proportion of charcoal iron. The mixture is heated in a furnace, and puddled into a ball, which is well worked up under a forge hammer. It is then drawn out under a tilt hammer, and rolled into strips of the required length and thickness, after which it is treated as above described. This material is much esteemed for its hardness and closeness of grain, but it does not possess the elegant marking and appearance of the Damascus twist. Stub iron for barrels was formerly made by putting a quan tity of old horse-shoes or stubs into an iron ring, welding them into a solid mass, and then rolling them out to strips of the requisite dimensions. Now a mixture of best wrought scrap, and sometimes steel scrap with stubs, is preferred, as giving more hardness and durability to the barrels. A description of the manufacture of cast-steel barrels will be found below, in connexion with military rifles. A sham-twist barrel is apt to impose on the purchaser ; plain iron is cheaper than twisted iron, and sometimes a thin coil of twist is rolled round a plain inner tube ; the whole is then welded together, and has all the appearance of a genuine twisted barrel. Other cheap barrels are made by rolling up strips of iron plate, and welding them together so that each barrel has a weld running down its whole length. As the breech end is thicker than the muzzle end, these barrels are usually mode in two lengths. In the rough state just described the barrels are sent Boring from the forge to the gunmaker, w r ho bores them carefully a ?d st: out to nearly the finished size. He then turns them pl down at intervals, obtaining correct surfaces by means of inside and outside gauges. The barrels are then "stripped" that is, turned down the whole length to correspond with the bore. For double guns two barrels are now brazed together, near the muzzle and near the middle. At the breech the barrels are separated by a "steel lump." The axes of the barrels are not quite parallel to each other, but are usually adjusted to cross at about 40 yards from the gun. When packed together, a rib is soldered on down the entire length, and they are sent to be proved at the proof280 GUN MA KING [SMALL ARMS. house of the Company of Gunmakers at Whitecliapet or Birmingham. The scale of proof is fixed by Act of Parlia ment, according to the size of the bore ; it is considerably more than double the ordinary shooting charge. For the provisional proof, muzzle-loaders have the breech screwed in before firing ; breech-loading barrels are pressed against a false breech. The second or definitive proof is less severe, and is carried out at a later stage, when the action of the breech-loader, or the percussion fitting of the muzzle-loader, is completed. The best stocks are made of English or Italian walnut, pieces of which reach the gunmaker roughly shaped. They are so cut that the grain shall run lengthways down the stock, and the wood is dried and seasoned to prevent warping. For expensive guns, much attention is paid to beauty of mottling and depth of colour. A con siderable variety of tools is employed in shaping the stocks and cutting out the beds for locks, processes which, for sporting pieces, are performed by hand. All parts of the lock except the plate are of steel, and reach the gunmaker hammered into shape. The lock-plate is of wrought iron, case-hardened. The parts are worked to fit by hand with a number of special tools. Bar locks are those which have a forward action, arranged so thab the main-spring fits under the bar below the breech end of the barrels ; back- action locks have the spring reversed, so as to extend down FIG. 2. Early breech-loader. C, pin fire cartridge; S, single grip. the hand or grip of the stock. The remaining portions ot the gun are termed the furniture. They are the heel plate which covers the butt, the break-off into which the breeching hooks for muzzle-loaders, the trigger plate, the trigger guard, the ham mers, the escutcheons, and bolt fastening the barrel to the stock, &c. For breech loaders the action is a most important part of the furniture. The ingenuity of gunmakers has devised an immense variety of actions, and every day sees progress made in strength and simplicity. M. Lefaucheux is entitled to the credit of inventing the modern sporting breech loader. He first hit on the combination of a pair of barrels open at the breech, playing on a hinge and abutting against a false breech (fig. 2), with a strong-based cartridge-case containing powder and shot ready for firing, and supplied with its own means of ignition. His early guns were found weak in the fastening of the barrels to the stock, while the mode of p IG 3 Central-fire igniting the charge was far from perfect. cartridge. It consisted of a pin passing through the upper part of the cartridge case, the point resting just above a percus sion cap placed at the centre of the base of the charge ; the hammer fell on the head of the pin, driving the point into the cap, and exploding the detonating composition. The gas was found to escape through the piu hole, the ex traction was sometimes difficult, and a fall on hard ground would occasionally explode the cartridge ; for these reasons the pin system was superseded by the central-fire method (fig. 3), in which the base of the cartridge case was made to hold a small anvil, on to which the cap was driven by a needle or striker passing through the false breech, and receiving the blow of the hammer. Fig. 4 shows a central- fire gun, having the action considerably strengthened by the double grip. In this system the extraction is accomplished Fia. 4. Central-fire Gun. C, central-fire cartridge ; L, lever ; W, washer ; S, screw. automatically, by a piece of steel fitting between the two- barrels, and so cut as to clip the rims of both cartridges. To this extractor is attached a rod which runs down between the barrels through a hole in the steel lump as far as the hinge; on opening the joint the rod is driven backward, carrying with it the head and forcing the cartridge cases out of the barrels. Guns on the central-fire system afford no indication of being loaded; extraction and loading are, how ever, so rapid and easy that every sportsman should invari ably withdraw the cartridges on laying down his gun, and seload on ae;ain taking the field. Hammers sometimes FIG. 5. Improved breech-loading action. catch in the brambles, or even in the clothes of the shooter ; even the double grip has been known to yield under tho effect of the heavy charges now used. The latest guns leave little room for improvement in respect to the action. Fig 5 shows one of the newest developments. The hammers are abolished altogether, the striker being a needle in the interior, which is driven against the cap of a central-fire cartridge by a spring when the trigger is pressed ; a lever on the top is pushed aside by the thumb, liberating the catch which holds the barrels against the false breech ; the barrels then drop from the hinge, and are open for loading. On raising the barrels, the action snaps to, and holds them fast; the dropping of the barrels causes an extractor to withdraw the empty cartridge cases. A key at the side regulates the cocking and safety of the lock and striker. SPORTING GUNS.] The sizes of barrels are designated according to the weight of the solid spherical lead ball which will just fit them, and hence their diameters vary inversely as the cube roots of their numbers. In the case of No 12 bore, the ball fitting it weighs 12 to the pound, and measures 729 in. in diameter. Ounce bullets (No. 16) fit a bore of 662 in. in diameter. Barrels were formerly bored cylindrically, but the experi ments of gunmakers led them to suppose that better shoot ing could be obtained by boring to shapes departing in various ways from the simple cylinder. The first modi fication introduced consisted in enlarging the breech end slightly for about 10 inches ; subsequently the last few inches at the muzzle were enlarged also, so that the barrel really consisted of two frusta of cones, having the smaller ends together, the position of the narrowest part, like many other matters, was dependent on the fancy of the gunmaker. Of late an attempt has been made to reduce the interior form of the barrel to something like a system, and several kinds of " choke " boring have been introduced. The object to be attained with a shot-gun is to so arrange the charge that the pellets shall be uniformly and thickly distributed round the mean trajectory, and shall occupy a small space longitudinally. In fig. 6 a side view of the charge as it passes through the air is given, ab being the mean trajectory. Exact experiments to determine the proportions of the cloud of shot fired from different guns do not exist, but, judging from observation, they will usually not depart greatly from those of the figure. In fig. 7 is seen the ap- ^ ,- pearance of the target , .. - after being struck by the charge. The test of . ", excellence is regularity of pattern, combined f " with penetration; that " > is, a circle of 30 inches . diameter should be so pitted by the shot at 40 yards range that gaps of the size of a small bird should no- where exist, while the individual pellets should retain force enough to penetrate a certain number of sheets of brown paper. As the shot pass along a barrel driven violently forward by the powder gas, it is probable that the edges of the charge are retarded by friction against the sides of the bore, so that the centre portion extricates itself rather sooner than the edges, and travels with a slightly higher velocity. Supposing the charge to retain an average velocity, on reaching the object fired at, of 300 feet per second, and the leading pellets to have gained 10 feet on the hindmost ones, so that the charge is distributed over a length of 10 feet, a period of time of - 3 th of a second will elapse between the blows of the first and last pellet. If the object be stationary, this interval will be almost imperceptible, and the pattern made on the target by the impact of the shot will exhibit no trace of it. But if the object be a bird flying across at the rate of 60 Fi 281 feet per second (about 40 miles an hour), it will traverse a space of 2 feet in the interval, and so will not receive the CARTRIDGE 12 BORE 13 BORE CHAMBER 2 8. FIG. 8. Plain choke. 1 12 BORE 13 BORE II BOREJ , i 13 BORI FIG. 9. Double choke. 1* 12 BORE 2 BORE 13s BORE 28.0 i FIG. 10. Greener s clioVe. charge at all in the manner shown on the target. Figs. 8, 9, 10 show some of the choke bores fancied by different makers. 1 The manufacture of sporting rifles does not greatly differ Sport from that of shot-guns. Greater strength and weight of rifles. barrel are necessary to resist the pressure of the charge, withstand the wedging action of the bullet, and deaden the recoil. The breech-closing action also demands greater strength, but the general arrangements are not different in principle. Rifles for sporting purposes differ from military pieces in being double-barrelled, and in requiring accuracy and penetration at short ranges, instead of a flat trajectory at very considerable distances. Hence they generally re semble the shot-guns in their action, and fire more powder in proportion to the weight of the bullet than military rifles. In fig. 11 the treble grip snap action is shown as specially devised for rifles firing heavy charges. In addition to the holding power thus provided, a piece is sometimes made to FIG. 11. Treble grip snap action. extend from the rib between the barrels, terminating in a projection which catches in a recess in the top of the false 1 No accurate or crucial experiments have as yet been carried out to determine the true action of these forms, but the editor of The Field is now preparing instruments and endeavouring to approach the sub ject in a scientific manner. The general principles, as far as they can be gathered at present, are, that enlarging or relieving the barrel slightly reduces the friction and allows the shot to acquire greater velocity, while choking the barrel at the muzzle has the effect of directing the outer pellets inwards, and so concentrating the charge.. XL 36 GUNMAKING [SMALL ARMS. breech, when the barrels are closed ; or the catch shown in fig. 5 may be adopted. Some makers, instead of using the hinge principle introduced by Lefaucheux, close the breech in other ways ; thus in the Henry action the barrel does not move, but is closed at the breech end by a sliding ver tical block, which is depressed for the admission of the cartridge by a lever underneath the trigger guard ; the striker passes through the block, which on being lowered extracts the cartridge. The power of a modern rifle is limited only by the power of the shooter to withstand the effect of recoil and to use a heavy piece. The momentum of the ballet forwards up to the time of its leaving the muzzle is equal (neglecting the weight and motion of the gas generated by the powder charge) to that of the gun backwards at any instant. Supposing the gun to weigh 150 times as much as the bullet, it will acquire a velocity against the shoulder equal to the 150th part of that acquired by the bullet. Practically it is this velocity which measures the severity of the recoil, and the heavier the gun and the more powerful the shooter the more momentum can he afford to impart to his bullet. This momentum may be composed of high speed and low weight, or of low speed and high weight. A light bullet starting with a high velocity travels fast at first and drops but little at a short range ; it speedily, however, suffers retardation by the resistance of the air, and would soon be beaten by a heavier bullet of the same diameter starting with the sarc.3 momen tum. The Express rifles carry out this principle with great complete ness, employing heavy powder charges and imparting very high spssd to a light bullet, so that a range of about 130 to 150 yards is traversed with a drop not exceeding 1 foot. Fig. 12 shows the nature of bullet generally used for these pieces; the hollow in the centre permits the lead to expand and flatten out on strik ing, inflicting a wound of great severity. Explosive bullets are also employed by some sportsmen. In fig. 13 are Fig. 12. FIG. 13. Rifle cartridges. shown rifle cartridges loaded ready for use. The solid brass-drawn case is now almost universally adopted, both for sporting and military purposes. The Martini-Henry rifles used by the British army, however, still use the soft brass-crimped case. Military Rifles. The principle of rifling small arms seems to have been discovered about the beginning of the 16th century, but does not appear to have been employed for warlike purposes till the middle of the 17th. In 1680 each troop of life-guards was supplied with eight rifled carbines. In 1800 the 95th regiment, now the rifle brigade, was armed with a 20-bore muzzle-loading rifle. The diffi culty of loading a rifle after firing a few rounds was the great obstacle to its use in the field. Several methods were devised of providing anvils at the bottom of the bore on which a loose ball dropped in could be hammered to fit the grooves, but the principle of expansion by the action of the powder was not brought forward till 1836, when Mr Greener submitted an egg-shaped bullet, having an opening at one end to receive a conical plug, which when driven home by the gas expanded the bullet into the grooves. Shortly after this the French chasseurs were armed with a rifle throwing an elongated bullet with a hollow-coned base. This was improved by Captain Minid, who added an iron cup to fit into the cone and expand it when forced home by the gas. For this cup a wooden plug was substituted in the three- grooved Enfield rifle in 1855. About this time Sir J. Whitworth brought forward his hexagonal rifling, the guiding idea of which was that every part of the hexagon except the actual corner should do its share of the work of giving rotation. He proposed for a barrel 39 inches long a bore of 45 inch, having one turn in 20 inches. This was intended to be suitable either for an expanding bullet, or for one possessing an easy mechanical fit. The length of the bullet was increased, and the form thus modified suffered much less from the resistance of the air than the previous patterns. The question of breech-loading for military weapons now began to assume importance. About 1841 the Prussians had adopted the needle gun, a breech-loader on the bolt principle. It was a rough weapon compared with the pieces lately introduced, but a great advance on any known at the time. A conical bullet rested on a thick wad, behind which was packed the powder, the whole being enclosed in strong lubricated paper. The detonator was in the centre of the hinder surface of the wad, so that to ex plode it a needle had to be driven forward from the breech through the base of the cartridge and through the powder. This was accomplished by the action of a spiral spring, when set free by the pulling of the trigger. This arrangement possessed many defects : the gas escaped freely at the breech ; the long needles rusted and broke ; the springs failed ; and the weight of the piece was excessive. Such failings caused the sterling merit of the principle to be underrated, and it was not till 1864 that a committee of officers recommended the introduction of breech-loading arms for general adoption in the British army. The triumph of Prussia in the Seven Weeks War with Austria in 1866 at once drew attention to the urgency of the case, and caused all civilized powers to re-arm their troops. In England the Enfield rifles (three-grooved expanding bullet muzzle-loaders) were converted into breech-loaders Ly the adoption of the Snider method, which consisted in cutting away 2 inches of the upper part of the breech end of the barrel so as to admit the cartridge, which was pushed forward into a chamber formed by enlarging the end of the bore. A block, opening on a hinge, was then shut down to fill up the space behind, forming a false breech against which the base of the cartridge abutted. The striker consisted of a needle passing through this breech block; when struck from behind by the hammer it was driven against a cap in the base of the cartridge, exploding the charge. By this means the existing rifles were rapidly converted, and the army was provided with a breech-loader of satisfactory efficiency should any emergency arise. Proposals were then invited, and a number of inventions submitted, the result of which was that in 1869 the combination of the Martini breech action with the Henry barrel was decided on for future manu facture, and the whole of the British army is now provided with these weapons (see figs. 14, 15, 16, 17). The general principles of manufacture are the same for all kinds of military breech-loading rifles. It will be sufficient to give the details of one in extenso. The manufacture of the Martini-Henry rifle, as carried out at the Government factory near Enfield, involves 2004 separate operations which have to be performed on each rifle before it is complete for issue. This number is subject to slight variations caused by changes of pattern from time MILITARY EIFLES.] GUN MAKING 283 to time. It will be sufficient if the principle of these operations are described, without entering minutely into details. The rifle is composed of three parts : the barrel, carrying the sights ; the stock, into which fits the cleaning rod ; the body, containing the lock and breech action. The soldier is also provided with a bayonet to fit on the muzzle. Fia. 14. Martini breech action (closed). Jarrel, The barrel is made of mild steel manufactured on the Siemens principle. Cylinders of this material, 16 inches long and 1^- in. thick, are supplied by contract, and tests are made of a proportion from time to time. These cylinders are first rolled in the factory to a long cone, having slightly greater dimensions than the exterior of the FIG. 15. Martini breech action (open). finished barrel. The cylinder is heated in the furnace and passed straight through a series of eight pairs of roll ; each pair is grooved to receive it, the grooves becoming narrower and shallower as each successive pair is reached. The pairs are alternately vertical and horizontal ; when they are in full work they can roll about 250 cylinders per hour. FIG. 16. Henry barrel. The cone is next placed between friction rollers ; these are set at a slight angle, so that in revolving they pass the cone along slowly. It emerges from their clutch polished with the compression, arid showing their action by a close spiral traced on the surface. We have now a solid piece of mild steel, slightly thicker than the barrel, fairly straight and thoroughly well-consolidated. 2 FIG. 17. Henry rifling (true size and magnified). The next step is to obtain true bearings for boring the interior and turning the exterior. The cone is placed in a clamp milling machine, and the ends milled down. This operation requires some judgment ; the milling-down of the ends must be so performed that the centres shall be ap proximately true centres ; that is, the amount of metal to be sub sequently turned down off the ex terior of the bar rel shall be about equal all round. The ends, when milled down, serve for bearings by which the cone is next held horizon tally, and drilled in a double-acting machine for in.; these act as centres when the barrel is placed vertically and drilled through from each end. Three tools are used, the last being of slightly greater diameter than the others. A shoulder is left in the centre to avoid the inconvenience of the tools from opposite ends not exactly meeting in the middle, as might be the case with the long slender drills necessarily employed. This shoulder is removed by a square tapered tool or " bit." We have now a cone slightly larger than the barrel, with a hole through it -433 in. in diameter. This hole is then bored out to 444 inch. Having now got a true inside, the next step is to obtain a true outside from it. The cone is placed vertically in a machine, the lower end fitting accurately on a pin, the upper end passing loosely through a hollow chuck, which revolves round a centre in truth with the centre of the pin and the axis of the bore of the cone ; the exterior of the cone, being slightly irregular, will be out of truth; sulphur therefore is melted and poured into the hollow chuck, filling up the space between the interior of the chuck and the exterior of the cone, and hardening on cooling. The chuck then holds the cone by the outside in truth, and serves as a bearing. The cone is then placed in a lathe, and two or three short cuts taken off the outside as bearings for the rough turning. This is called "spotting." It is now rough and finish turned, the outside becoming concentric with the inside ; and the cone becomes a barrel. It is next tested for truth of interior. Two tests are Testing employed, the first being that by shading. The barrel is barrels placed in a rest, so arranged that the eye looking through the tube sees the straight line of the top of a window cutting horizontally across the aper ture a little above the cen tre. If the barrel is accu rately straight and brightly polished, the shadow thrown by the dark window-frame down the tube appears as in fig. 18. The interior circle shows the window as seen through the barrel, with the dark frame cutting across ; FI G. 18. Testing by shading, the next circle shows the shadow extending in a cone from A to B and C. This shadow is quite dark, and AB, AC are quite straight. BC is a portion of the arc cutting off the shadow sharply at a point half-way down the barrel. 284 There are two outer circles extending to the eye, and approximately resembling the sketch in shading. If the barrel is untrue in interior surface, or bent, the cone will at once lose its regularity, and the sides AB, AC will no longer be straight. Should they be irregular, the barrel is "set" by striking with a hammer or ebonite mallet across a set ting block. The barrel is next placed in a machine, and a horizontal spindle is run through it ; on this spindle are two close- fitting gauges, one in the centre and one at the end ; the barrel is then caused to revolve on the spindle, and an indicator with a long arm recording small graduations is inserted at the free end between the spindle and the barrel ; any irregularity of turning is multiplied 200 times by the long arm, and becomes at once apparent. After passing these tests the barrel is finish-turned ; the back sight is soldered on and screwed, and the fore sight is brazed on; the size of bore is then gauged, after which the process of polishing is completed and the barrel is ready for rifling. Rifling. The rifling consists of seven grooves of the form shown in fig. 1 7. The twist is such that the bullet makes one complete revolution while travelling 22 inches ; that is, one turn in 49 calibres of 45 in., to employ the phraseology generally applied to the rifling of cannon. Each groove is cut separately by a tool which acts when pulled ; it forms the groove by five successive -cuts, being forced to project a little more at each cut; it thus passes thirty-five times up and down the barrel to complete the rifling, which can be done in half an hour The size of bore is now finally tested; it must lie between 449 and 451 inch. The rifling is similarly tested, and the twist gauged. Cartridge The breech end of the barrel is next chambered out to chamber receive the cartridge, which is of the kind known as " bottle- shaped." The exterior of the breech end is of "Nock s" form, the upper surface being a flat, true to the bore. This flat guides all the fittings ; the barrel is placed in a machine true to the flat, and the sights are gauged for line and elevation. No allowance is made for the deflexion due to twist of rifling, it being very slight. The barrel is lastly screwed at the breech end to fit the body. Each barrel is twice subjected to proof by powder, once before rifling, once after. Sixteen are placed in a cast-iron frame ; a temporary steel screw, furnished with a vent, closes each breech end, which rests against a leaden bar. The barrels are loaded from the muzzle ; a train of powder ignited by a cap fires them simultaneously ; the bullets are caught in a hollow cast-iron receiving frame, shaped like the shell of a snail. The charge for the first proof is 7J drs. ( = 205 grs.) of powder and a bullet weighing 715 grs., secured by a half-inch cork wad forced down over it. The second proof is the same, except that only 5 drs. ( = 137 grs.) of powder are used. The service charge is 85 grs. of powder with a bullet of 480 grs. The barrel when finished is browned by being coated with browning mixture, and caused to rust in a steam tank ; it is then brushed with wire brushes. This process is repeated four times, after which the exterior is oiled over. The browning mixture consists of Proving Spirits of wine 5 oz. Spirits of nitre 8 ,, Tincture of steel 8 ,, Nitric acid . . , . . 4 , , Corrosive sublimate 4 oz. Blue vitriol 4 ,, Water 1 gal. Stock. The stock is in two parts, the butt and the fore-end. They are of Italian walnut wood, and are supplied roughly shaped. They are tested for straightness of grain ; weight, as indicating strength; " shakes" or cracks ; "galls," caused by injuries over which the wood has grown ; saltness (which would cause absorption of moisture and consequent rusting), bv putting a shaving into a solution of nitrate of silver ; [SMALL ARMS. and also for appearance. Those accepted are thoroughly seasoned by keeping, or dried in a desiccating chamber, warmed by hot air ; they then go to the shaping machines, where they are cut to size by revolving cutters, making 4000 revolutions per minute, and are afterwards turned in copying lathes, hollowed out by copying gouges, and bored to take the fittings. They are then tested, machined, hand- finished, and oiled up. The body is of mild steel ; it is stamped out from the BO bar ; it is then drifted through by a slightly tapered bar carrying a succession of cutters on it. The front part of the body is then screwed to suit the screw on the barrel, so that when home it shall fit accurately to the breech end. The lever, and indeed all parts except screws and springs, are stamped out of solid bar. Each part is milled by machinery to a correct fit ; every fitting is interchangeable, and nothing is marked for selection to fit anything else. Each part is browned in the same way as the barrels, or blued. On completion all parts are taken to the assembling room, where they are fitted together, screwed up, and turned out as finished rifles ; after which they are taken to the practice ground, and tested for accuracy and extraction of cartridge by being fired from a rest at a target, the range being 500 yards. The bayonet consists of a steel blade welded to a Ba wrought-iron socket. Steel of a superior quality being used, it is supplied in bars, is cut into lengths, and is welded by the aid of borax to a short rod of rolled iron. The two arc so put together as to form a right angle ; the steel bar is put into a " Rydering " machine, which gives it a great number of rapid blows, and shapes it roughly into a blade. It is then rolled and cooled gradually under charcoal and coal-dust for annealing purposes. The socket is then drilled, and the blade ground. They are then bent into position and become a bayonet. Turning and finish-boring complete the sockets, while the blades are fine-ground, hardened, tempered, tested, and polished. The sockets are then browned and adjusted to the rifles. About 1400 operatives are employed at the Government factory ; each Martini-Henry rifle costs about 48s., all expenses reckoned; and to render the establishment thoroughly remunerative, the out-turn should be about a rifle a week per man. The systems of breech-loading muskets employed by Ya different nations are shown in the following table : of kel Country. Nature. "o | X Action. Austria "Werndl .. r > Block rotatinf sideways. Bavaria Werder 4 Falling block. Denmark England France . . . Remington Martini-Henry Gras 5 4 4 Block hinged to rear, sup ported by a cam. Falling block. Slidinf bolt. Germany Mauser 4 Do. Italy Vetterli 4 Do. (magazine gun). Russia Berdan 5 Block hinged to front (old). Spain Remington 5 Sliding bolt (new). Block hinged to rear, sup Sweden .. Do

• ,

ported by a cam. Do. Switzerland Vetterli 4 Slidingbolt(magazinegun). Turkev Martini-Henry 4 Falling block. United States Springfield 5 Block hinged to front. It will be noticed that the Vetterli gun, used by the Italians and Swiss, is a repeater or magazine gun. It contains a supply of eleven cartridges, arranged in a tube running under the barrel, and forced by a spring into the loading position one by one, as the previously fired empty one is extracted. The arm can thus fire twelve rounds with great rapidity without reloading ; it can also be used as an MILITARY RIFLES.] GUNMAKING 285 ordinary breech-loader, a fresh cartridge being inserted at every round, and the magazine kept constantly full. This is no doubt a great advantage under certain circumstances, but entails grave inconveniences. Thus the Vetterli gun, with magazine full, weighs just half as much again as the Martini-Henry, and gives less energy to its bullet at the muzzle in the proportion of 5 to 8, a proportion which increases to the disadvantage of the magazine gun as the range increases. Still, for a melee, and at short ranges, the Vetterli is no doubt a very formidable piece. These considerations have led the Government of the United States to make trials of a number of magazine guns, of which one, the Hotchkiss, has been selected for adoption. The working of it is shown in fig. 19. The magazine is contained in the stock, and holds five cartridges, a sixth bsing in the chamber ready for loading. These cartridges are the same as those used for Government Springfield rifles ; they are pushed successively into the loading position by a spiral spring till the magazine is empty, or a fresh cartridge FIG. 19. Hotdikiss Magazine Gun. can be inserted after each round as in an ordinary breech loader. The action of bringing the knob-handle upright and withdrawing the bolt extracts and throws out the emptied cartridge to the side ; the next cartridge is then pushed up into the loading position by the spring, and is forced into the barrel when the handle presses the bolt forward ; this action also cocks the piece, but the striker cannot reach the cartridge till the knob-handle is turned down, and the bolt thus locked in position. The weight of the piece fully loaded is 9-i lt>. Trials of this weapon are about to be made by the English Government. Of all the military rifles adopted by the various Govern ments, the Martini-Henry is the most powerful; the practical test it underwent in Turkey, where a cheap gun of this pattern was supplied on con-tract by an American firm during the war of 1877-78, was most satisfactory. Pistols. These handy little weapons were formerly made as single or double-barrelled smooth-bored muzzle-loaders, and their system involved no departure in principle from the ordinary firearm of the day. The introduction of the revolver as a practical weapon was a great step in advance ; the iclei is old, and roughly constructed weapons on the same plan have long existed in museums of old arms; Colonel Colt of the United States revived it, and is the father of the modern revolver. In his pistol a revolving muzzle-loading cylinder contains a number of chambers, usuilly five or six, bored from the front parallel to the axis ; the back of the cylinder is left solid, and forms the breech ; a nipple is screwed into each chamber. As the cylinder revolves, each chamber arrives at the top, and is then opposite to a barrel ; the pistol is cocked by the thumb, an action which locks the chamber against the barrel, so that the two form a continuous bore ; the trigger is pulled in the usual way, and the hammer brought clown on the upper nipple, exploding the charge in the top chamber. The action of recocking brings the next chamber into position. When on half-cock, the cylinder revolves freely. Since Colt s time great improvements have been made in these handy weapons ; the trigger was made to cock the hammer, turn the cylinder, and fire the charge by one continuous draw ; this arrangement enabled the shooter to fire all the shots very rapidly without lowering his hand : the strength of mainspring required, however, rendered it very difficult to shoot with any degree cf accuracy, especially as the exact moment when the hammer would fall was hard to estimate. A second improvement gave the shooter the choice of cocking the hammer and firing it in the usual way, if he preferred it. The next step was to make the chambers breech-loading, by boring them right through, and packing the powder and bullet in a strong based cartridge, carrying its own ignition. In pistols constructed on this plan the chamber arriving at the top is brought against a false breech through which the striker is driven by the hammer. In the latest pattern of this pistol, the cylinder and barrel open away from the false breech on a hinge underneath ; the action of opening throws out the empty cartridge-cases. If the user is on horseback, he thrusts the barrel muzzle downwards into his breast, belt, or holster, the hinge remaining open ; fresh cartridges are taken out of the pouch and placed in the chambers ; the breech is closed sharply on the hinge "and is held by a snap-catch ; the pistol is then withdrawn ready for use. All this can be very quickly done with one hand at full gallop. MACHINE GUNS. This term comprehends all weapons made to fire a rapid succession of bullets from a stand or carriage, so that, while requiring but two or three men to work them, they may throw in a fire equal to that of a detachment of infantry. In the Franco-German war of 1870 a species of mitrailleur was largely employed, and when used under Mitrs favourable conditions attained fair success. It consisted leur - of a number of barrels (usually 25 or 37) secured in a frame round an axis, and parallel to it. The barrels were open at the breech, and were loaded by a disc pierced to correspond with them containing a cartridge in each chamber. This disc was placed against the breecli end of the barrels, the false breech containing the strikers was FIG. 20. Galling Gun. held firmly against it, and the whole of the charges were exploded at once. This arrangement had many defects. The recoil of so many charges fired simultaneously required strength and weight ; at short ranges the bullets all went to the same spot; the number of rounds could not be regulated at pleasure ; and only volleys could be fired. The Gatling machine gun, which first appeared in the United Gatlii States, was vastly superior to the mitrailleur, and speedily gun- obtained entrance into the armies of most of the civilized powers. Figs. 20 to 2 G show the general construction of the weapon. In fig. 20 the Gatling is reicly for firing. A block of ten barrels is secured round an axis, which is fixed in a frame a a. On turning the handle h (fig. 21), the 286 [MACHINE GUNS. spindle gg causes the worm/ to act on the pinion iv, making the carrier, which consists of ten grooves or chambers M the axis and barrels revolve. A drum T (figs. 20, 24, 25) (fig. 23) corresponding to the ten barrels. The construction of the lock is shown in fig. 26. It consists of a bolt, through Fig. 21. Fig. 22. is placed on the top at the breech end of the barrels over a hopper, through a slot in which the cartridges drop into Fig. 24. Fig. 25. which passes a striker driven by a spiral spring. AAAA is a cam, sloping as in the drawing, which it must be under stood represents the circular construction opened out and laid flat. As the barrels, carrier, and locks revolve, the slope of the cam forces the locks forward and backward alternately. At position I. the cartridge has just fallen into the carrier, the lock and bolt are completely withdrawn. At positions II., III., IV., the cam is forcing them forward, FIG. 26. Lock of Gatling Gun. so that the bolt pushes the cartridge into the barrel. At IV. the cocking cam II begins to compress the spiral spring, releasing it at V. Position VI. shows the cartridge just after firing ; the extracting hook, omitted in the previous MACHINE GUNS.] GUNMAKING 287 positions, is here represented in the act of clutching the base of the cartridge case, which is withdrawn as the locks retreat down the slope of the cam, till at X it falls through an aperture to the ground. The line ab marks the com mencement of the rifling. In fig. 20 the drum T consists of a number of vertical channels radiating from the centre. The cartridges are arranged horizontally, one above the other, in these channels, bullet ends inwards. The drum revolves on the pivot b (fig. 23), and the cartridges fall through the aperture B. When all the channels are emptied, a full drum is brought from the limber, and sub stituted for the empty one. Each barrel fires in turn as it comes to a certain position, so that by turning the handle quickly an almost continuous stream of bullets can be FIG. 27. Nordenfelt Machine Gun. 1-10, parts of frame; 11, breech plug; 12, striker; 13, extractor; 14, cartridge receiver; 15-18, 23-31, lock and trigger parts; 19-22, locking action; 32-35, load- ing action; 36-39, cartridge receiver; 40, cover ; 41-44, parts of hand-lever ; 45-49, traversing action; 50-55, elevating and trailing action ; 56, 57, hopper and slide. ejected. An experimental pattern of Gatling has been lately tried, fitted with a multiplying arrangement which could be made to fire nearly 1000 shots a minute. In fio-. 21 an automatic traversing arrangement is shown, which can be put in or out of gear as desired, and by means of which the amount of traverse can be regulated. The spindle gg turns the wheel A, projections on which act on the arm F, and traverse the breech through a small arc, thus spreading the bullets laterally over the required front. Effective though this piece is for land service, especially in defending approaches, it is scarcely suitable for the navy, as the mobility of the boats or vessels carrying it causes immense waste of ammunition, it being impossible to lire more than a, few rounds at the object before an important irden- change of direction occurs. The Nordenfelt machine gun, tgun. shown in figs. 27 to 31, is found specially suitable under these circumstances. The barrels are here placed horizon tally, and have no movement. A box containing the locks, bolts, strikers, and spiral springs, one of each correspond ing to each barrel, 28, moves straight back- Fig. 29. wards and forwards when worked by the handle of the lever on the right. When the box is drawn back the cartridges fall from the holder on the top into the carriers simul taneously. When the box is pushed forward the bolts push the cartridges into the barrel, cocking-catches compress the spiral springs, the lever releases the catches one after the other at very minute intervals of time, and the cartridges are fired in rapid succession. In this piece, careful aim can be taken from a moving platform, and at the right Fig. 30 Fig. 31. moment the barrels can be fired at the object almost simul taneously ; they could be made to fire at the same instant, 288 G U N M A K I N G [ORDNANCE. but in tills case the advantage of being able to fire single shots would be lost, and the recoil would be increased. This gun would probably never be able to fire with such extreme rapidity as the experimental form of Gatling men tioned above, but it could be made to fire six or seven hundred rounds a minute. It is generally considered that a machine gun should be able to fire easily two hundred rounds in half a minute. ORDNANCE. ilnance. The manufacture of ordnance is a much more scientific and complicated study than that of small arms. As the forces increase in magnitude and intensity, while the ultimate strength of material remains constant, the nicety of adapt ation of means to ends grows pari passu with the guns. In producing a piece of ordnance, two distinct sets of conditions are involved those belonging to its actual construction, and those by which its proportions are regu lated. In constructing a gun, the material must be so selected and disposed as economically and safely to sustain the effect of the forces developed by the charge ; in design ing a gun, it is necessary to know the nature and direction of the forces which will combine to produce the desired ballistic results. The two sets of conditions are as distinct as those involved in the separate operations of writing and printing this article. nstruc- CONSTRUCTION. Nearlyall the accurate knowledge asyet a - obtained of the true action of gunpowder has been acquired within the last twenty years. The general idea previously held was that the explosion was instantaneous, and that the more violent the powder the greater would be the velocity of the projectile, The mode of proving the quality of the explosive was to place a small quantity in a short mortar, and to measure the distance to which it projected a light shell a test altogether wrong in principle, as will be shown later on. No accurate idea had been formed of the true pressure of the powder gas on the bore during discharge ; but it was understood that a gun was subjected to two principal strains orstresses a circumferential tension tending to split the gun open longitudinally, and a longi tudinal tension tending to pull the gun apart in the direc tion of its length. !omo- When guns are made of cast metal, and are, in fact, jneous homogeneous hollow cylinders, a limit is soon reached lus beyond which additional thickness is practically useless in giving strength to resist the circumferential tension. Supposing the metal employed to be incompressible, each concentric layer would take up a strain on discharge inversely proportionate to the square of its distance from the axis of the bore. Every metal, however, is compres sible as well as extensible, and hence the exterior always affords more support to the interior than the foregoing rule indicates. The great aim then of a gunmaker is so to select and arrange his material that the exterior shall take up as much as possible of the strain thrown upon the interior. In America, Captain Rodman introduced a method of casting guns hollow and cooling them down from the interior, so that the inner portions being first solidified were compressed and supported by the contraction of the outer parts when they subsequently cooled down. Thus, on discharge, the compressed inner portions expanded under the action of the powder gas to or beyond their natural diameter, throwing at once the strain on the outer portions which were already in a state of tension. But however well cast-iron may be disposed, it is naturally too weak and brittle for use with heavy guns, and those nations which employ it thus do so because it is comparatively cheap and easy to manufacture, and not because it is the best material. Austria and Russia have of late years made light guns of bronze cast in chill, and subjected to the wedging action of steel mandrils driven through the bore. The several layers of the metal are thus placed in a state of tension as regards the exterior, and of compression as regards the interior. At the present day systems of building up guns have been devised so that each portion of the metal is made to bear its fair share of the strain. The longitudinal tension is usually less important than the circumferential stress. It is considered to be provided against in homogeneous guns if the metal is as thick over the bottom of the bore as round the end. The strain is now measured by calculating the total pressure of the powder gas on the bottom of the bore, and comparing it with the area of the transverse section of the gun at the same place. This is not absolutely correct ; but, practically, the chief modes of gun construction now adopted leave a considerable margin of strength in this direction. Sir William Armstrong first successfully employed the Built- principle of initial tensions for all parts of a gun. In his guns, system, wrought-iron coils are shrunk over one another, so that the inner tube is placed in a state of compression and the outer portions in a state of tension, an endeavour being made to so regulate the amount of tension that each coil should perform its maximum duty in resisting the pressure from within. Further, he arranged the fibre of the several portions so as to be in the best positions for withstanding the pressures. It must be noted that wrought-iron bar is about twice as strong in the direction of the fibre as across it. He therefore constructed the exterior of the gun of coiled bars of wrought iron welded into hoops and shrunk one over the other, thus disposing the fibre to resist the circumferential strain. These outer coils were shrunk over a hollow cylinder of forged iron, having the fibre running lengthways so as to resist the longitudinal strain. Yithin this cylinder or forged breech-piece was placed a steel tube, gripped in like manner by shrinkage. This grand Slu-in principle of modern gun construction is carried out by turn- age. ing the inner coil in a lathe to an exterior diameter slightly greater than the interior diameter to which the outer coil is bored. The outer coil is expanded by the application of heat, and slipped over the inner one. It contracts on cooling, and if the strength of the two coils is properly adjusted, the outer will remain in a state of tension, and the inner in a state of compression. On this view, the ideal gun would be constructed of a vast number of exces sively thin rings so shrunk over each other that, on discharge, each should be equally strained. An attempt has been made by Mr Longridge, M.I.C.E., to approximate to this condition by winding steel wire under tension round a steel tube. This system, though possessing much ingenuity, has never made way, and might possibly be found wanting in longitudinal strength. Great success attended the early introduction of the coil principle. Guns of considerable size were made : the largest weighed as much as 23 tons, and projected a COO-lb shot with a fair velocity. It was found, however, that much difficulty attended the accurate shrinking of a number of thin rings, and that occasionally one or more of the outer ones would be strained to cracking, while the inner ones were intact. The original mode of construction was therefore modified, as experience was gained in the Govern ment factory at Woolwich. Acting underGeneral Campbell, R.A., Mr Fraser, M.I.C.E., thickened the coils, and extended their use to the breech-piece, it being found that the longi tudinal disposition of the fibre in that part was not required to sustain the longitudinal strain, and that the steel tube forming the bore was better supported by coils. The manufacture of ordnance at Woolwich and Elswick may be briefly described as follows. Steel cylinders, slightly larger than the exterior dimensions of the inner CONSTRUCTION.] tubes, are suppliel by contractors. They are tested for quality of metal, and toughened after being bored by being raised to the temperature shown by the tests to be most suitable to the particular cylinder, and then plunged in oil. They are subsequently tested by water pressure at 4 tons Fig. 32. p3r square inch. The tubes are not bored quite through for muzzle-loaders ; a solid end is left to form the bottom of the bore. The rest of the gun is made of wrought iron. The material is chiefly received from the contractor in the form of wrought scrap, but a certain proportion of iron piddled in the works is used also. Blooms of these materials are rolled into flat bars, which are fagoted together and rolled into long bars of the section required for the part of the gun for which they are intended. These bars are then placed in a long narrow reverberatory furnace, i-^- 1 Fig. 34. foiling, and raised to a bright red heat. When ready for coiling, one end is drawn out and fixed to a revolving mandril, which pulls the bar out and winds it into a coil, like rope round a capstan. Sometimes a second bar is wound round outside the first coil ; in this case the mandril is made to r Fig. 35. revolve in the opposite direction. The coil is next placed upright in a reverberatory furnace, and raised to a white or "welding" heat. In this state it is placed under a steam hammer, and welded till it becomes a compact hollow cylinder. On cooling it is bored and turned to the proper r Fig. 36. dimensions. Two parts of the gun are made of forged iron (not coiled), the cascable screw which supports the breech end of the tube, and the hoop which carries the trunnions. The latter is either welded to the outer coil or shrunk on. Figs. 32-39 show the method of building up Woolwich Fig. 37. Juilding ordnance as exemplified in the 80-ton guns. The various coils are hooked together by shoulders to prevent slipping or distortion from the shock of discharge. Thus, in fig. 36, shoulders are turned on the exterior of the breech-piece and inside the IB coil; the latter is expanded by being raised to a dull red heat and slipped over the tube from the muzzle end. The expansion enables the shoulders to pass, 289 and on cooling they grip each other as shown, while the IB coil contracts on and slightly compresses the part of the tube within it. A method of strengthening and utilizing as rifled guns Con- some of the old cast-iron ordnance of the service has been verte( largely employed to supply pieces of secondary power and ^ uns excellence for land fronts and for practice. It was brought forward in its present shape by Sir W. Palliser in 1863, and is now being much used in the United States gun factories. The cast-iron block or gun is bored out to the Fig. 38. requisite dimensions, and a tube of coiled wrought iron is thrust into it; no shrinking is here employed, but a toler able fit is ensured by accurate turning. When fitted, the tube is secured by a collar screwed in at the muzzle ; a plug of iron passes through the under side of the gun into the tube near the trunnions to prevent any shift of position. The tube is in two parts, the breech end being turned down and a second tube shrunk over it. The bottom of the bore is formed by a wrought-iron cup, which is forged and stamped into shape under a steam hammer. A screw is Fig. 39. cut on the outside of the cup and inside the end of the tube; the cup is then screwed tightly home. The tube is next severely tested by water pressure, after which the second tube is shrunk on. The whole tube is then fitted into the cast-iron casing, the greatest care being taken that the breech end bears firmly home. The gun is now ready for rifling, an J, after that operation is performed, undergoes proof by firing heavy charges, which expand the tube closely against the cast-iron envelope, which then takes up the strain and affords the necessary support. The relation between the powers of the three classes of guns will be gathered from the following comparison : Nature of Gun. Weight of Gun. Weight of Pro jectile. Weight of Charge. Calibre. Energy of Projectile at 1000 yards. Energy of Projectile at 2000 yards. cwt. It). tt>. ins. foot-tons. foot-tons. Cast-ison 68-pr., 1 smooth bore, . | 95 C8 16 812 298 136 Palliser 80-pr , converted from V 100 80 10 6-30 C02 488 68-pr. above, . ) Wrought - iron ") 7-in. Woolwich > 90 ii5 22 j 7-00 1042 814 gun, . . .) The great German gunmaker, Krupp, employs nothing Steel but steel in the manufacture of his ordnance. His earlier guns pieces were bored from solid blocks of this metal forged under heavy hammers. They were homogeneous, and therefore the exterior did not assist the interior to bear the strain of the powder gas on discharge to the extent which scientific methods of construction admit. Still the excellent quality of the material enabled the artillerist to gat results from these pieces which have been surpassed only by the coil guns, and by Krupp s later productions. As, how ever, progress was made and the ratio of power to weight increased, it was found necessary to introduce a system of building up for steel ordnance also, and Krupp adopted the principle of shrinkage to which the English guns owed so XL - 37 GUNMAKING rupps mstruc- much. The interior of the recent German gun is a steel tyke ag m ^ Q Armstrong construction, but it is very much thicker and forms the body of the piece, instead of being chiefly used to provide a sound surface for the bore. It is thickest over the powder and shot chambers, tapering towards the muzzle (fig. 40). Over the thickest part, and in some guns over a considerable portion of the chase, hoops of cast steel are shrunk on, the shrinkage being adjusted FIG. 40. Section of Krupp Gun. to bring the strength of the outer hoops into play to sup port the body of the gun on discharge. The number of hoops depends on the size of the gun and the severity of the strain it has to withstand ; they are usually much more numerous than the English coils, and the section of a heavy Krupp gun presents somewhat the appearance of a stone wall It is believed that the steel is not toughened in oil, but the details of manufacture have not as yet been made public. Steel of the excellent quality employed by Krupp is un doubtedly a stronger material than wrought iron ; its present trustworthinesss is, however, of late date, and it has hardly gained the general confidence accorded to wrought iron. Possibly the method of construction adopted by Krupp, containing as it does a number of unwelded joints, scarcely permits the several parts of the guns to support each other as efficiently as is the case with the magnificent forgings of the coil system ; be this as it may, the German pieces, though made of stronger and more ex pensive material than the English ones, are just as heavy for any given power, proportions and ammunition being similar. In France and Italy a combination of cast iron and steel has been introduced with a view to economy. The interior of the gun is a moderately thick steel tube as in the coil guns ; over this is a thick cast-iron body, corresponding to the steel body of the Krupp guns. On the exterior are shrunk steel hoops. Sir J. Whitworth uses his fluid-compressed steel for the manufacture of ordnance. He forces massive hoops over a central tube, and over one another by hydraulic pressure or by shrinkage. Mr Vavasseur employs Firth s crucible steel for his guns, which are built up somewhat in the same way as Krupp s. He also uses exterior coils of wrought iron in some patterns. /Systems of Loading. The comparative advantages of breech-loading and muzzle-loading for ordnance on service are fully discussed in the article GUNNERY. We have now to mention the principal modes of closing the breech, either permanently as in muzzle-loaders, or temporarily as in breech-loaders. The former is comparatively a simple matter. When the whole gun, or the interior of it, is formed of cast metal, iron, bronze, or steel, the block is merely bored to the required depth, and the end left un- bored to form the breech. Should the inner part of the gun be formed of wrought material, such as coils, it becomes necessary to close the end with some device which shall render it gas-tight and strong. Several kinds of cups and plugs have been tried for this purpose, the most successful of which is the cup already mentioned in the description of the converted guns. When we come to the temporary closing of the end of the bore demanded by breech-loading, a far more difficult problem presents itself. This problem has been more or less satisfactorily solved in a great variety of ways, but it will be sufficient to examine the three principal types or systems of breech-loading employed in modern artillery. They are popularly known as the Armstrong, the Krupp, and the French systems. The Armstrong system is the earliest of these in point of Arm- date. In it a slot is cut through the top of the breech of stron i the gun into the tube at A (fig. 41) ; a breech block (fig. Jj" 43), through which the vent is driven, is dropped into this ^^ I itu i ] - T 1 P ft 1 >5 . i /~^ 1 ~ l 7 * s | V17 - 7 T| i j 1 i J c ! II S---15V75 3 t u:-..-. . _. T*-* ~- B* (a v < S2: a FIG. 41. 7-inch Armstrong Breech-loader. slot, and is pressed firmly against the bore from behind by the breech screw (fig. 42), which is provided with two powerful lever handles for the purpose. Where the breech block, or vent piece, as it is usually called, presses against the lip of the bore, both surfaces are of copper, and are re newed from time to time as channels are worn through between them by the rush of the escaping powder gas. There are many guns, from 6-pounders to 7-inch, made on FIG. 42. Breech Screw. FIG. 43. Vent Piece. this plan in the British service, and at the time of their intro duction they constituted a great advance in gun construc tion. Experience in the field and at practice has, however, revealed many grave faults in them. No joint consisting simply of two abutting surfaces can be made so tight as to prevent the gas from escaping on the discharge of the piece ; the pressure in the powder chamber is so great that a con siderable expansion takes place for the moment, and per mits a fan of flame to flash out. The eroding effects of gas in motion at high pressure are extraordinarily destructive, and constant necessity for repair arises from this cause. It has also been found that in rapid firing the breech screw may be too quickly forced home, nipping the vent piece before it has fallen into its proper position ; the end of the bore is then not sealed, and important and perhaps danger ous accidents occur. Moreover, even with moderate-sized ordnance, the vent piece becomes too heavy for convenient lifting. In the Krupp system (fig. 44), a slot is cut through both sides of the breech of the gun ; in this slot, in the latest patterns, runs a cylindro-prismatic wedge, or, in other words, a wedge of D section, the round side to the rear. The flat side forms the bottom of the bore. For loading, the wedge is pulled out to the left side of the piece as far as the stop will allow it to go, the shell and cartridge are thrust up the gun from behind, the wedge is pushed in, and is pressed hard home and secured by an ingeniously- contrived screw with powerful handles. As was mentioned with regard to the Armstrong system, no amount of pressing home and securing would by itself be of any avail in preCONSTRUCTION.] GUN MAKING 291 venting escape of gas at the breech, and a special arrangement is therefore provided for this purpose (fig. 45). The end of the bore is enlarged, and into the recess thus formed fits a Broadwell ring, against which the face of the wedge abuts when forced home. The ring is so formed that it must always fit against the wedge, and be pressed firmly to it by FIG. 44. Krupp s breech action, cylindro-prismatic wedge, the action of the gas on firing. This is accomplished by making the recessed surface of the gun and the exterior surface of the ring portions of a sphere. In spite of the theoretical perfection of the system, and the excellence of manufacture attained, it has always been found that after a time after firing a very variable number of rounds gas would begin to escape, and then speedily cut a channel between the ring and the wedge. Krupp has fully recog nized this, and has been succcessful in minimizing and localizing the injury thus caused. The gas has two ways of escape : it can pass either between the ring C and the body of the gun D, and so out to Y ; or from X to Y. Several forms of Broadwell ring have been tried by Krupp ; the form shown in fig. 45 is now in use. When the gun is fired the gas acts on the rounded surface of the ring C, press- ing it down hard against the Fl0 " 45. -A steel facing-plate ;BB . . , , copper discs ; C, steel Broadwell lacing -plate A, and also ex- ring . D; body of gun; E, wedge; panding it against the body X, interior of gun ; Y, exterior of the gun D. The tendency of uu - of the gas is also to expand the body of the gun away from the ring, and many bronze guns have been destroyed from this cause, having expanded more than the ring was able to follow. A recess is cut in the exterior of the ring, partly to give it greater spring and partly to afford a relief channel for any gas that may have forced its way in. The form of ring here shown appears to have overcome the efforts of the gas to escape in this direction. Having stopped the gas from getting round the outside of the ring and injuring the gun, we have now to consider the results of escape from X to Y. A channel cut through here would disable ring and wedge, which, though not so bad as disabling ring and gun, would yet be productive of much inconvenience. The insertion of the steel facing-plate A at once saves the wedge and localizes the injury. It allows, moreover, of the introduction of copper discs behind the plate, for the purpose of making up for wear, compres sion of metal of wedge, &c. Two relief channels are cut round that surface of the ring which abuts on the facing- plate. Spare Broadwell rings and facing-plates are supplied with the guns ; should wear set in and escape of gas ensue, the defective fittings can be removed from the gun and new ones inserted in a couple of minutes. Each set should last on the average for several hundred rounds. In the French system no slot is cut in the gun (fig. 46). Frein The breech is closed by a screw plug from the rear, which breec swings on a hinge to the side when withdrawn, The male ^ screw on the plug and the female screw in the gun are "" divided circumferentially into six parts, of which three have the threads cut away, so that the surface is alternately screw and plain cylinder. When the threads of the plug coincide with the plain parts in the gun, the plug can be moved straight in or out. When pushed in, one- sixth of a turn en gages the threads, which thus give half the bearing of an ordinary screw. This is called the interrupted screw system. The plug FIG. 46. French breech action, is larger than the interrupted screw. bore, so as to afford room for the shell and cartridge to be thrust in. The end of the bore is recessed to take a ring against which the end of the plug abuts, somewhat as in Krupp s guns ; or a cup of steel is fixed on the end of the plug, which is slightly convex ; the pressure of the gas drives the flat back of the cup firmly against the con vex surface, bending out the lips, which are at the same time pressed against the sides of the gun by the gas. This method has been lately introduced by the Elswick Company. It is difficult to award superiority to the Krupp or the French system. Each appears to possess some little advan tage over the other, and both have attained great success. The Krupp system has undergone the more thorough testing in the field, and has the merit of allowing the parts which become damaged by the escape of gas to be replaced with greater ease and quickness. The French system, on the other hand, takes up less of the gun, so that in a piece of given length the bore may be upwards of one calibre longer than with Krupp s. In the French system, also, the breech- fittings are less exposed to damage by the enemy s fire, being behind the gun instead of at the side. DESIGNING. A gun, like all other machines, must be Gun designed to fulfil certain definite conditions. Its projectile s g may be required to pierce a given thickness of armour at a given distance ; or weight of piece may be the limit, and it may be wished to throw the most powerful shell or shrapnel to a given distance with a given elevation, con sistent with that limit. To work out problems of this nature, it is all-important to possess an accurate knowledge of the action of the charge inside the bore. By means of the Noble chronoscope and the crusher gauge (sec GUNNERY), this knowledge is obtained, and we shall now explain how the indications of these instruments are employed to assist in determining the proportions of ordnance. Gunpowder is not properly so much an explosive as a substance burning and giving off gas with great rapidity. It offers in this respect a marked contrast to gun-cotton, dynamite, and other true explosives. If one of these agents be detonated, the detonation is immediately carried through the mass, whatever its size, and the whole at once turns into gas. Gunpowder, on the other hand, as far as is known at present, cannot be detonated, but simply evolves its gas by burning in layers from the outside to the inside. Thus a large grain will take longer to burn up and become 292 GUN MAKING [OFO>:S T ANCE. entirely converted into gas than a small one will ; lience ! the effect of enlarging the grains is to render the action of j the charge less violent, the composition of the powder being | the same in all gun charges. The projectile is driven out of ressure the bore by the pressure of the gas on its base, that is, on an area which varies with the square of the calibre. The weight of projectiles of similar form varies with the cube of th3 calibra. Hence the larger the gun the heavier will be the column of metal or projectile driven by each square inch of its base; and the greater must be either the pressure applied, or the tima of its application, if a given velocity is to be attained. The great object of the gunmaker is to obtain t!i3 highest possible ratio of muzzle velocity to breech prassure. His ideal would be a charge so arranged that a pressure equal to the amount the gun is constructed to bear should be uniformly maintained till the shot has left the nvjzzb. Science is still a long way from this, but has done a good deal towards it iu the last few years. A charge of ganpowder, composed of service ingredients in service pro portions, exploded in a closed vessel at a density of I OO (equal to that of water), sets up a pressure of 43 tons per square inch; at a density of 75, of 23 2 tons; at 50, of 1 1 8 tons. Supposing a gun cartridge to be rammed home to the density of water, and entirely converted into gas bofore the projectile began to move, the pressure in the bore would rise to 43 tons per square inch at the breech, an I fall towards the muzzle, as the travel of the shot afforded increasing room for expansion behind it. The column of metal to be moved, even in the heaviest pro jectiles yet known, is only a few pounds to the square inch of base, while the maximum pressure of the powder gas is measured in tons ; it is clear therefore that the shot must get under way at some period antecedent to the setting up of the maximum pressure. In a breech-loader, where the projectile has to be forced through a bore slightly less than its greatest diameter, it will be detained longer than in a muzzle-loader, where it moves freely away, but the difference is insignificant as regards the present argument. The result of tli3 shot s early motion is that space is at once given for expansion, and the normal 43 tons is never reached. Before these matters were fully understood, badly-proportioned charges of violent powder were found sometimes to set up what are known to artillerists as " wave pressures," which were dynamical in character, being caused by rushes of gas from one end of the charge to the other, so that the gauges indicated far higher pressures at the ends of the powder chamber than in the centre. This has now been overcome, and a great increase of both power and safety has been ob tained. Several important improvements have been made of late years ; the principal ones are three in number : (1) a great stride was made in the manufacture of powder when pebbles, prisms, and H-inch cubes were introduced; (2) the discovery of the beneficial effect of "chambering," that is, of boring out the powder chamber to a greater diameter than that of the rest of the bore; (3) tho method of "air spacing" the cartridge, so that a certain Air sj weight of powder should have a certain definitespace allotted in - to it, irrespective of the actual volume of the powder grains. Thus in the 80-ton gun powder cubes of 1 ?> in. edge are used, having an absolute density a little over T75, or about 15 7 cubic inches to the pound. If these grains were rammed tightly home in a silk-cloth bag, the space occupied behind the shot would be 24 - G cubic inches per pound ; as actually used, an air-space over and within the cartridge is left, so that the space behind the shot amounts to 34 cubic inches per pound. This density would set up a pressure in a closed vessel of 26 6 tons per square inch, but the relief afforded by the shot s motion reduces it to about 19 tons per square inch. The effect of chambering out the end of Chan: the bore where the powder lies is practically to permit a in - small gun to consume effectively the charge of a larger one. The cartridge is shortened, and the mechanical conditions of burning are greatly improved, so that, with large charges, higher velocity with lower pressure is obtained from a chambered than from an unchambered gun. The above information is derived from the indications of the crusher gauge, which registers the pressure of the gas at various pnrts of the bore. The chronoscope measures the rate at which the projectile acquires velocity during its travel from the breech to the muzzle. Knowing the increment of velocity at any point, we can calculate the amount of pressure required to produce this increment, and thus con firmation is obtained of the accuracy of the records obtained by the crusher gauge. The following table gives the increase obtained at successive stages in the development of the power of the 80-ton gun, which was first under-bored for experiment, and gradually brought to its present dimensions : Table showing Experiments with 80-ton Gun. Powder, Service P 2 (-incli cubes). Calibre. Diam. of Chamber. Weight of Charge. Density of Charge. Weight of Projectile. Mean Pressure in Chamber. Muzzle Velocity. Muzzle Energy. Muzzle Energy per Ton of Mean Pressure. 1 enetrating Power into Armour at 1000 yds. Thickness of Armour which would be pene trated at 1000 yds. ins. ins. ri>. cubic ins. per 11). It). tons per sq. in. f.s. ft. -ions. E Y ft.-tons per in. of shot s circumf. Ins. 14-5 14-5 220 25-6 1259 22-9 1502 19,637 857-5 373 22-7 15-0 15-0 2-20 25-6 1466 23-8 1423 20,577 864-6 383 23-1 15-0 15-0 290 30-0 1466 22-4 1511 23,205 10o6 433 25-1 15-0 16-0 310 30-0 1466 22-5 1553 24,493 1089-0 457 25-8 16-0 16-0 350 32 1703 20-4 1505 26,740 1311-0 466 261 16-0 18-0 425 34-0 1703 19-3 1588 29,745 1543-0 523 28-1 16-0 13-0 460 1 31-4 1703 191 1626 31,527 1651-0 545 30-2 Mild prismatic powder (German). It will be observed that each improvement has tended to facility of consumption of increased charges, so that, while the pressures are diminished, the penetrating power of the projectile is augmented, a heavier and more destruc tive shell being driven through thicker armour. The manner in which the various principles, of which an explanation has been above attempted, are practically applied is laborious and complicated ; the conditions are often con flicting, and the ultimate dimensions of a piece of ordnance H commonly a compromise. A couple of simple examples will illustrate the modus operandi. Suppose that it is required to design a gun which shall not exceed a given length, but shall throw a projectile capable of piercing a given thickness of iron at a given range. There are several formulae of a more or less empirical nature for calculating the perforating Perfo power of a projectile moving with a known velocity. Pene- t< tration is by some regarded as a punching action, by some as a wedging action ; probably it is a compound of the two. Recent experiments carried on with the very high velocity of about 2000 f. s. have thrown some doubt on the sound ness of any of the formulae. That generally used iu England is as follows : DESIGNING.] GUN MA KING 293 Let W = weight of projectile in tons ; r = radius of do. in inches ; v = velocity of do. in feet per second ; Vv 2 = energy of do. in foot tons t = thickness of plate perforated in inches; then 1-xr This formula tells the gun-designer what energy is neces sary to overcome the resistance of the plate. Guided by experience, he assumes for the moment a striking velocity; the other component of the energy, the weight of the projectile, is then directly arrived at. The proportions of armour-piercing shell are the same for all guns, so that the weight guides the dimensions, and the calibre of the gun follows. Should this appear to be in no way unsuit able to the length already laid down in the conditions, the gun-designer calculates the loss of velocity in the given range and from the striking velocity deduces the muzzle velocity and the muzzle energy. The excellent Work labours (Researches on Explosives) of Captain A. Noble, lone by F.R.S., of Elswick, and Professor Abel, F.K.S., have shown in ~ how to calculate the amount of work done by a pound of powder for every volume of expansion its gas undergoes; the results of many careful experiments and much intricate calculation are embodied in the accompanying table, which B B ~C~ Total work Gun c Total work Gun where B=content powder is capable where B=content powder is capable of bore in cub. in., of performing per of bore in cub. in., of performing per and C=vol. of Ib of charge burned. and C=vol. of Ib of charge burned, charge at 277 in foot -tons. charge at 27 7 in foot-tons. cub. in. per Ib. cub. in. per Ib. TOO o-o 4-0 82-1 1-02 1-9 4-5 87-1 1-04 3 8 5-0 91-4 1-06 5-5 5 5 95-2 1 -OS 7-2 6-0 98-6 1-10 8-9 6-5 101-7 1-1-2 10-4 7-0 104-6 1-14 11-9 7-5 107-2 i-16 13-3 8-0 109-6 1-13 14-7 8-5 111-8 1 "JO 16-1 9-0 113-9 1-25 19-2 9-5 116-0 1-30 22-1 10-0 117-8 1-35 24-9 11-0 121-2 1-40 27-4 12-0 124-2 1-45 29-8 13-0 127-0 1-50 32 -0 14-0 129-6 1-55 341 15-0 132-0 1-60 36-1 16-0 134-2 1-70 39-8 17-0 136-2 1-80 43-1 18-0 138-1 1-90 4G"2 19-0 139-9 2-00 49-1 20-0 141-6 2-50 60-6 25-0 149-0 3-00 69-3 30-0 154-8 3-5.0 76 -3 35-0 159-7 affords the means of determining the total work performed by any charge in any gun. A certain portion of this work is expended in heating the gun and projectile, in giving rotation, and so forth ; the remainder appears as the energy of translation of the shot on leaving the muzzle. Large guns realize a greater proportion of the total work than small ones ; the gunmaker knows very approximately by experience what percentage may be expected from certain classes of ordnance with certain descriptions of powder. Roughly the factor of effect may be put within the following limits: for mountain guns, 45 to 50 per cent ; field guns, 60 to C5 per cent.; medium guns, 70 to 80 per cent.; heavy guns, 85 to 95 per cent. The method of calculation will be best understood from an example. Suppose a charge of 425 ft> of P 2 powder is to be fired from the SO-ton gun chambered to 18 inches diameter; the projectile weighs 1700 ft>, and the space behind it is 14,450 cubic inches. The whole content of the bore is 60,400 cubic inches, and the volume of the charge is (425 x 27 7) 11,773 cubic inches, the number of expansions therefore is 5 13 ; the table shows that powder gas expanding to this extent from a density equal to that of water can perform work amount- ing to 92 4 foot-tons per ft). Since, however, the charge burns up in and has to fill (425 x 34) 14,450 cubic inches before doing work, the energy due to this extent of expan sion (1-227) is lost, and 17 7 foot-tons per ft) must be deducted, leaving (92 4- 17 7) 74 7 foot-tons per ft) as the total work the charge is capable of performing under these conditions. It is known from the preliminary tests of the powder that in the 80-ton gun between 92 and 95 per cent of the total work will be realized. Hence the energy of the projectile will lie between 29,210 and 30,155 foot-tons, and its muzzle velocity between 1581 and 1600 f. s. A reference to the table on p. 292 will show that the result actually arrived at lies nearly midway between these limits. In this manner the charge required to impart the necessary energy to a shot of given weight hi a given length of bore, and, conversely, the length of bore which will contain the re quisite number of expansions of a given charge, are easily found ; hence the charge required to produce the necessary energy is readily found ; the air-space and the dimensions of the powder chamber follow, and the inside of the gun is settled. The gun designer now has to put walls round his bore. Guided by the knowledge previously mentioned as derived from the crusher gauge and the chronoscope, he lays down the pressures at each point of the interior, and calculates the amount and strength of the metal to be used, according to the special system of construction employed, and thus the exterior of the gun is settled. To give another instance : let it be required to construct the most powerful howitzer that can be made for the siege train. The conditions are given thus : recoil (of piece only) must not exceed 20 feet per second ; weight of piece must not exceed 70 cwt.; limiting purposes are to breach at 1500 yards, with not more than 5 elevation, and to bombard at 5000 yards, with not more than 35 elevation. A piece weighing 70 cwt. and running back at 20 f. s. velocity gives 156,800 units of momentum (in pounds and foot- seconds); the initial momentum of the gun in recoiling is practically equal to the momentum of the shot on leaving the muzzle. Hence the shell must have 156,800 units of momentum, which may be composed of high velocity and light weight, or low velocity and heavy weight. For breaching purposes, accuracy and penetration are essential qualities ; a shell varying in length from two and a half to three times its diameter will be suitable for the purpose. We have now a neat problem in ballistics, viz., To find the calibre of a shell of the proper length, of such a weight that, with the muzzle velocity required to give a range of 1500 yards at 5 elevation, the muzzle momentum shall be 156,800 units. This problem is readily solved by the methods indicated in the article GUNNERY, and it is found that a shell 80 in. in diameter, weighing 170 ft), and having a muzzle velocity of 940 f. s., will be slightly on the safe side of the limits. Proceeding in a similar manner, a shell 8-0 in. in diameter, weighing 230 ft), starting with a velocity of 675 f. s., satisfies the conditions of bombard ment. The calibre being thus settled, the proportions of the piece remain to be worked out. As there is no difficulty in obtaining a velocity so low as 940 f. s. with a small charge and low pressure, the length of the bore and the disposition of the metal can be adjusted to suit, not only the strain of discharge, but the conditions of service. In the gun now under consideration, the bore is made as long as possible, and the weight of metal thrown as far forward as possible consistently with preserving due strength at the breech. The reasons for this are threefold : finst, the longer Actic f d < ngni 294 GUN MAKING [ORDNANCE. riflia; the bore the less is the breech pressure required to produce a given muzzle velocity, and the less is the maximum strain thrown upon the studs, gas check, or other rotating agent ; next, the more forward the general disposition of the metal, the farther from the breech end will be the centre of gravity, j and consequently the trunnions, a position which favours steady shooting and absence of jump; thirdly, a siege ! howitzer, being always fired under cover, is little exposed except near the muzzle, which should therefore be made as strong as possible to avoid injury from anything less than a direct hit by unburst shell. Rifling. Spherical projectiles fired from smooth-bored guns seldom or never pursue the mean trajectory. The centre of the ball s figure will rarely coincide exactly with the centre of gravity, and the pressure of the air during flight will then act with unequal effect on different parts of the surface. This inequality will be increased by accidental imperfections or roughness. The difference between the diameter of the bore and that of the projectile is termed " windage "; when this is considerable, it is a principal cause of error in shooting, as the ball rebounds from side to side against the walls of the piece as it is driven along, its actual direction of departure depending on the effect of the last bump before it leaves the muzzle. Accuracy of manufacture may greatly mitigate these errors, but will never entirely remove them ; it is therefore found necessary to cause the projectile to rotate rapidly round an axis coincident with the axis of the gun ; by this means the inequalities in the action of the pressure of the air, due to the imperfections above mentioned, take effect in all direc tions in turn as the projectile rotates, and hence neutralize ea^h other. Extending this principle, the stability im parted to a shot by its moment of rotation is such that elongated projectiles can be employed and driven point first j .at high speed through the air. The course of the projectile from the time of its leaving the muzzle to the end of its flight belongs to GUNNERY (q.v.). Here we have to con- Princi- sider the modes in which the interior of the gun is made to pies of impart rotation to the projectile. Rotatkm is usually ex pressed in angular velocity ; a shot is said, in popular language, to make so many turns per second. Mathemati cally, the unit of angular velocity consists of rotation through the unit of circular measure in one second; the unit of circular measure is the angle subtended by an arc equal to radius, viz., 57 17 44" 48" . If we call this angle w, a complete rotation will be expressed by 27rw. In consider ing the energy stored up in a shot s rotation, or, what is the same thing, the work done in producing that rotation, the weight of the projectile W, and its radius of gyration p, must be taken into account. The energy of a travelling body is ; the weight of a rotating one is supposed to be concentrated at the end of the radius of gyration ; then if O be the angular velocity, the velocity of a travelling body will correspond with pfi in a rotating one, and the energy W of rotation will be expressed by p 2 fi 2 . The propor tions of service projectiles differ for different guns, the thicknesses of sides and base and the shape of head varying ; but roughly for common shell the value of p may be taken as 40c (d = diameter), for Palliser projectiles as - 38cZ, and for shrapnel as 36c For artillery purposes a pro jectile is said to turn once in so many calibres, that is, to make one complete revolution in travelling a distance equal to so many times the diameter of the bore. Supposing a given length of groove in the bore to make a known angle with a line parallel to the axis of the gun, determining the arc through which the surface of the shot must turn while advancing the length of the groove, it is evident that the angular velocity attained by the shot will entirely depend on the velocity of translation or forward movement. Again, the greater the diameter of the bore the less will be the proportion borne by the arc turned through to the whole circumference ; consequently the bigger the gun the less the angular velocity of the projectile, if the angle of rifling and the velocity of translation remain constant ; the velocity of rotation of a point on the surface will, under these condi tions, always be uniform. It is generally considered that with studded muzzle-loading service projectiles, having a length equal to about 2 to 3 times their diameter, the velocity of rotation of a surface point of about 110 f. s. is sufficient to keep them steady, allowing for loss of spin by atmospheric friction up to any probable range. Supposing the interior of the gun to be opened out and laid flat, the groove (of a uniform twist) will be straight, and since the shot guided by it makes a complete revolution in n calibres, the angle made by the groove with a line parallel to the gun s axis may be expressed by tan -. In designing the ?t piece, the muzzle velocity is determined on, and also the velocity of rotation to be communicated to the projectile; the combination of the two fixes the final angle of the groove. Now it is easy to see that the spin of the shot on leaving the bore depends only on the conditions immedi ately preceding. The rate at which the work of giving rotation is done during the travel of the projectile from breech to muzzle is an entirely different question. If a shot be rotating, its tendency is, putting friction aside for the moment, to continue to rotate with the same velocity. No work is done in keeping up this rate of rotation, but work would be done in accelerating or retarding it. Thus in apportioning the work done on the shot in giving rotation Umf< at different parts of the bore, we have to consider, not the aiul i actual angular velocity, but the increments of angular "^ velocity. The work then can be distributed at pleasure over the whole length of the groove, by varying the angle it makes with a line parallel to the gun s axis, as it runs along the bore. Supposing, as before, the interior surface of the gun to be opened out and laid flat, then OU (fig 47) will represent a groove having a uniform twist, that is Fig. 47. making a constant angle with a line OM parallel to the axis of the piece. O denotes the commencement of the rifling at the breech end of the bore, UPM the muzzle. Guns are rifled with any number of grooves exceeding two, but it is not necessary to consider more than one. With the groove OU, every increment of angular velocity im parted to the shot is due to an increment in the velocity of translation ; and therefore the pressure between the sides of the grooves, and the studs, gas check, lead coating, or whatever fitting on the shot is employed for the purpose, bears a constant relation to the pressure of the powder gas on the base of the shot driving it forward. The table given below shows the result of this with great clearness. In order to mitigate the unevenness of strain, recourse was had to the increasing twist ; and a curved groove was employed which, when developed as in fig. 47, forms the parabola OP, begin ning at the point O, parallel to OM, and terminating at P, parallel to OU. The equation to OU is x=py that to OP is x 2 = py. Since OP is a parabola having its vertex at O, and since the tangent at P is parallel to OU therefore RIFLING.] GUN MAKING 295 UP = PM, which shows that the shot, though rotating in either case with equal angular velocity on leaving the muzzle, has, up to that moment, with the parabolic twist turned through an angle half as great as would be the case with the uniform twist. The table below exemplifies the principle on which curves of rifling are, or should be, constructed. The first three columns speak for themselves ; the fourth is arrived at by multiplying the area of the shot s base by the gas pressure per square inch recorded on the gauges, and given in the 5th column. Columns 6 and 7 are worked out from formulas due to Captain Noble of Elswick ; in column 6 the pressures due to a uniform twist are given. Prea It will be seen that they bear a constant proportion to the on pressures of the gas recorded in columns 4 and 5, and that S 100 the maximum rises to a considerable height soon after the shot has begun to move, while at the muzzle little work is done. In column 7 the calculations are made to suit a curve consisting of a portion of a parabola, starting from the vertex where the groove is parallel to the axis of the piece, and rising to the required twist at one foot from the muzzle, thence proceeding uniformly. In this curve the maximum strain is greatly reduced, the pressure gradually Table showing Pressures of Grooves on Studs in the 38-ton Gun, with various Curves of Rifling. Charge, 130 ft. Cubical Powder of l 25-inch edge. Projectile, 800 K>. Calibre, 12 "5 inches. Travel of Shot through Bore. Time of Travel. Velocity acquired. Pressure on Base SQuare mc h O f of Shot. Base Pressure on Studs with Uniform Twist of 1 turn in 35 Cals. Pressure on Studs, Parabola, Twist to 1 in 35 Cals. Pressure on Studs, Semi-Cubical Pura- bola, 1 in 200 Cals. to 1 in 35 Cals. ft.

sees. ooooo f.s.

tons. 2000 (estimated) tons. 16 3 tons. 79-3 tons.

tons. 31-4 1 00143 140 2221 -3 181 88-1 1-65 22-6 5 00273 474 3320-3 27-0 131-6 15-6 59-8 1-0 00360 676 2060-6 16-8 81-7 26 -3 61-3 2-0 00490 869 1394-1 11-4 55-3 421 65-1 3-0 00598 987 1095-0 8 9 43-4 531 66-3 4-0 00695 1074 908-8 7-4 36-0 61-95 66-3 5-0 00785 1142 746-4 6-1 29-6 687 85-0 6-0 00871 1195 668-3 5-4 26-5 75-0 647 7-0 00953 1242 592-8 4-8 23-5 80-3 63-9 8-0 01032 1277 499-4 4-1 19-8 83-3 61 9-0 01109 1309 421-9 3-5 16-7 86-2 58-95 10-0 01184 1335 355-6 2-9 14-1 88-2 56-6 11-0 01258 1355 265-1 2-2 10-5 88-1 53-95 12-0 01331 1369 1887 1-5 7-5 87-3 48-8 13-0 01404 1379 131-6 1-1 5-2 ( 86-4 ) ( 5-2 i U5-2) 1 5-2 | 14-0 01476 1385 120-9 I O 4-8 4-8 4-8 rising with the increase of twist. The figures are derived from another formula worked out by Captain Noble. Column 8 shows the pressures required to give the neces sary rotation when the curve of groove is a semicubical parabola, having for equation x% = py. In the instance chosen, the early part of the curve is rejected, and it starts from 1 turn in 200 cals., arriving at the required twist at a foot from the muzzle as before. The figures are derived from a calculation worked out on the principle devised by Captain Noble. Here the maximum is yet further reduced, and some approach to uniformity of strain is made. The diagram in Plate IV. shows the pressures graphically. Let R=- rotation pressure between studs and grooves ; G = gas pressure on base of shot ; yu = coefficient of friction ; h = pitch of rifling ; k = tan. of angle made by groove with plane traverse to axis ; <f> = angle turned through by shot ; 6 = angle made by groove with line parallel to axis ; p = radius of gyration ; z-= travel of shot along v = velocity of shot ; W M = mass of shot = ; r = radius of shot. Then in a uniform twist (z = bore ; in a parabolic twist in a semicubical twist hr(k - .G; 2V z p Vz(3Vz + 2>) Lieut Younghusband, E. N. , gives the following formula, which is applicable to curves of any equation, and will be found much handier than the above by those familiar with differential calculus :

rl + tan 2 0) - tan (r 2 - A radical difference exists between the rifling of muzzle- loaders and that usually employed for breech-loaders. When the projectile has to be pushed down the gun from the front, it must be smaller than the bore ; when it is thrust home from behind, it may be rather larger than the bore. Hence the earlier muzzle-loading shells were provided with ribs or studs which fitted in the grooves, and guided the projectile in its rotatory course ; while the earlier . breech-loading shells were coated with lead, into which the lands of the bore bit sharply as the powder gas forced the projectile between them. All rifled ordnance were formerly rifled with a uniform twist ; indeed, it is clear that where ribs are cast or fixed on the projectile, or where they are formed in the soft envelope by the first action of the grooves, no alteration in the angle of rifling is possible, since the ribs can only make a constant angle with a line parallel to the axis of the piece, and cannot fit a groove making a varying angle with it. The smaller and earlier muzzle-loading rifled projectiles were fitted with two rows of studs, front and rear, and equal in size, so that a front and rear stud travelled in each groove, and practically con stituted the ends of a rib. As the guns grew, it was found Mod that the great strain of giving rotation at starting fre- of g quently forced the bronze studs out of the recesses machined for them in the sides of the shells, and scooped away the driving edges of the grooves even when the gun lining was of steel. The shell might have been cast with ribs on them, but certain difficulties of manufacture stood in the way, and the excessive strain would still have ex isted though its effects might have been mitigated. The increasing twist was therefore devised, and the rows of studs increased in number from two to three in the larger natures of projectiles. Three studs are allotted to each 10 296 GUNMAKING [ORDNANCE. groove ; the rear one is the largest, the front one the smallest. They are so placed that the line of their loading sides is parallel to the angle made by the groove at the breach, while the line of their driving edges is parallel to the angle made by the groove at the muzzle. In Plate IV. fig. 1 shows their position when the shell is home, and also when about to leave the bore. Thus, theoretically, the middle and leading stud should never come into play till the last moment, and the rear stud should do all the work of rotation. Practically, however, the rear stud, being of bronze, wears down against the edge of the hard groove ; the centre stud obtains a bearing ; the wear continues, and the leading stud takes up its share of duty ; so that all three really act during the passage of the projectile through the bore. This method of employing the increasing twist necessitates wide grooves, and is unsuitable for small guns. A different plan therefore was devised to meet their case. Two rows of studs, front and rear, were so arranged that each ran in a groove of its own. The curve of the grooves Studs, belonging to the rear stud began at 0, and reached the final angle at a distance from the muzzle equal to the dis tance between the front and rear rows, after which it pro ceeded in a straight line. The curve of the grooves belong ing to the front studs began at 0, at a distance in front of the commencement of the other grooves equal to the dis tance between the rows, and reached its final angle at the muzzle. Thus the two curves were alike, but one was always a constant distance in front of the other, and every stud acted through the entire length. Fig. 2 in Plate IV. shows the position of the studs when the shot is home, and also when it is about to leave the bore. Muzzle-loading rifling had reached this stage of progress at a time when the great wear caused by the rush of gas over the shot necessitated the adoption of some method of sealing the escape. After many trials, it was found that a flanged copper disc fitted on to the base of the projectile would expand under the first pressure of the gas, and cut off the windage completely. This saved the wear of the guns, and added to their power. It was found, moreover, Gas that the flanges of these " gas checks " expanded in the checks, grooves, and being firmly attached to the shell afforded an additional means of giving rotation. The next step was to remove the studs altogether, using a smooth projectile, and substituting many small grooves for few large ones. This metho.l of giving rotation has been adopted in all recently- designed pieces, and appears likely to give entire satisfaction. When muzzle-loading guns were first rifled, many attempts were made to give rotation by expanding projectiles, but they proved unsuccessful, because at that time the increas ing twist was not known, and the action of a violent powder and the uniform twist was that the rotator had to expand into the grooves, and at the same instant to communicate a rapid spin to the shell. It was unable to combine these operations, and the projections driven out by the gas could never settle to their work, being constantly cut down by the edges of the grooves. The result was that the shell " stripped," and left the bore without regular rotation. In the case of the twist which begins at 0, the projections have time to expand comfortably, and adapt themselves to the shape of the grooves before they are called on to perform the work of rotation. On the other hand, since the gas presses out the flanges against the bore and into the grooves, and affords them support in this position, it is desirable that its pressure should correspond with their pressure on the driving edges of the grooves. This would be exactly met by the uniform twist, but that is inadmissible for the reason just given. The parabola, on the other hand, throws the principal rotating strain forward towards the muzzle, where the gas pressure is least (Plate IV.). The case is practically met by the semicubical parabola, which is the curve adopted in the 80-ton gun. While progress was thus being made in the rifling of muzzle-loaders, the rival system had not remained inactive ; the use of lead coating had been found Lead to involve a loss of power in the projectile as regarded both coatir the amount of bursting charge or bullets carried, and the penetration into armour, on to the surface of which the lead flew forward in a splash, when the shell struck. Moreover, the lead envelope would not lend itself to the exigencies of the increasing twist. To meet these difficulties, two under cut rings were machined round the smooth projectile, one near the base, the other near the shoulder. Into these slots were pressed stout copper wires, the rear one bringing up Coppi the diameter of the shell beyond that of the bore, so as to bands take the rifling when forced through the piece on discharge, the front one just fitting the lands, but not entering the grooves, so as to rotate irrespective of them, and thus keep the fore part of the shot steady. Projectiles thus fitted are more effective than the lead-coated ones, and are adapted to auy twist of rifling. The latest breech-loaders iirnde by the Elswick Company use the new arrangement described above for muzzle-loaders the smooth shell with a gas check on the base. This appears to be the best form of projectile, and has the advantage of suiting either system. A few words on the section of groove best suited to various pur poses will conclude the subject of rifling. The rotation is impressed on the projectile by a force acting tangentially to the surface. This principle would be represented in its extreme form by making the section of the shell to resemble a cog-wheel, the grooves and lands of the gun being bored to fit. With muzzle-loading systems where windage has been necessary, the sides of the projections on the projectile, and of the grooves in the bore, have been sloped to enable the projections to run up the sides of the grooves, and so distribute the windage equally all round. The extreme form of this principle is Lancaster s oval bore, the section of which departs but slightly from a circle. All attempts at "centring" the projectile by sloping the bearings tend Cent- to convert it into a wedge, which expends that part of the ril) K- force resolved radially in a crushing action on the shell, and a rending action on the gun. The slope may, however, be made of such a degree as to cause the projectile to centre fairly without exercising any important effect on the bore. In breech-loading systems, where the lands bite into the rotator, the driving edge strikes the projectile in, or nearly in, the prolongation of the radius, care being taken that the points of action are as many as possible consistently with leaving enough material between to stand the wear and the strain. Where gas checks expand in the grooves, these should be broad and flat, so that a complete fit and a strong projection should result. The driving edges should here also form a prolongation of the radius of the projectile. Conclusion. What may be the future of firearms it is ConcI impossible to predict, but it seems probable that the limit sion - of power will be found to lie in the recoil. F^r shoulder guns, methods of withstanding increased velocities may be devised, but the weight of springs, pads, <fec., will prevent the soldier or the sportsman from carrying this principle very far. For ordnance, the field artillery appear even now to be very near the limit of what power can be gained consistently with high mobility. Siege and heavy guns will no doubt gain by the increased application of hydraulics; but it is difficult to see how progress can go much further except in the matter of size, to which there appears to be practically no limit. Accuracy may be improved by moro perfect methods of range finding, but, as regards the actual shooting of the guns, it is already in advance of the difficul ties of atmospheric irregularity, which affects the smaller projectiles greatly. The reader who wishes to study the subject closely and technically is referred to the list of works

given at the end of the article on GUNNERY. (E. M.)

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