the wire is indicated on a dial, and the headstock, containing the drum of wire, is capable of being moved along the bed G by a leading screw H, driven by a belt through variable speed cones I; the belt is moved along the cones by forks J, traversed by screws K, which in their turn are actuated by chain belts from the hand wheel L. The traversing speed is regulated to suit the speed of winding by moving the belt along the speed cones.
The wire is rectangular in section, 0·25 in. wide and 0·06 in. thick, and after it has been wound on to the gun it presents a very even surface which requires little further preparation. The diameter over the wire is gauged and the jacket or other covering hoop is carefully bored equal to this, if no shrinkage is to be allowed; or the dimension is diminished in accordance with the amount of shrinkage to be arranged for.
The gun is built up, after wiring, in the same manner as a gun without wire, the jacket or other hoop being heated in the vertical gas furnace and when hot enough dropped into place over the wire, cooled by the ring of water jets at the end first required to grip and kept hot at the other, exactly as before described.
The machine arranged for rifling modern guns is very similar to that employed for the old muzzle-loaders; it is a special tool used in construction only (fig. 21), and is in reality a copying machine. A steel or cast-iron bar J which forms the copy of the developed rifling curve is firstRifling operation. made. The copying bar—which is straight if the rifling is to be uniform but curved if it is to be increasing—is fixed, inclined at the proper angle, to standards K on the machine. The cutting tool is carried at one end C of a strong hollow cylindrical rifling bar B, the other end of which is fixed to a saddle M. This is moved along the bed of the machine by a long screw N, and the rifling bar is consequently either pushed into the gun or withdrawn by the motion of the saddle along the machine. During this motion it is made to rotate slowly by being connected to the copying bar by suitable gearing I. It will thus be seen that the cutting tool will cut a spiral groove along the bore of the gun in strict conformity with the copy. In most English machines the cutting tool cuts only as the rifling bar is drawn out of the gun; during the reverse motion the cutter F is withdrawn out of action by means of a wedge arrangement actuated by a rod passing through the centre of the rifling bar, which also pushes forward the cutter at the proper time for cutting. One, two or more grooves may be cut at one time, the full depth being attained by slowly feeding the tool after each stroke. After each set of grooves is cut the rifling bar or the gun is rotated so as to bring the cutters to a new position. In some foreign machines the cut is taken as the rifling bar is pushed into the gun.
Fig. 21.—Rifling Machine.
Rifling is the term given to the numerous shallow grooves cut spirally along the bore of a gun; the rib between two grooves is called the "land." Rifling has been known for many years; it was supposed to increase the range, and no doubt did so, owing to the fact that the bullet havingRifling. to be forced into the gun during the loading operation became a mechanical fit and prevented to a great extent the loss of gas by windage which occurred with ordinary weapons. Kotter (1520) and Banner (1552), both of Nuremberg, are respectively credited as being the first to rifle gun barrels; and there is at the Rotunda, Woolwich, a muzzle-loading barrel dated 1547 rifled with six fine grooves. At this early period, rifling was applied only to small arms, usually for sporting purposes. The disadvantage of having, during loading, to force a soft lead (or lead-covered) ball down a bore of smaller diameter prevented its general employment for military use. In 1661 Prussia experimented with a gun rifled in thirteen shallow grooves, and in 1696 the elliptical bore—similar to the Lancaster—had been tried in Germany. In 1745 Robins was experimenting with rifled guns and elongated shot in England. During the Peninsular War about 1809, the only regiment (the "Rifle Brigade," formerly called the 95th) equipped with rifled arms, found considerable difficulty in loading them with the old spherical lead bullet, from the muzzle. In 1856 Russia made a large number of experiments with a rifled gun invented by Montigny, a Belgian; this was not a success, but in England the guns invented by Major Cavalli, in 1845, and by Baron Wahrendorff in 1846, obtained some measure of favour. Both these guns were breech loaders. The Cavalli gun had a bore of 6.5 in. diameter; it was rifled in two grooves having a uniform twist of 1 in 25 calibres, and the elongated projectile had two ribs cast with it to fit the grooves, but no means were taken to prevent windage. The Wahrendorff gun had an enlarged chamber and the bore of 6.37 in. diameter was rifled in 2 grooves; the projectile had ribs similar to that for the Cavalli gun; but Wahrendorff had also tried lead-coated projectiles, the coating being attached by grooves undercut in the outside of the shell. In 1854 Lancaster submitted his plan of rifling; in this (fig. 22) the bore was made of an oval section which twisted round the axis of the gun from the breech to the muzzle; a projectile having an oval section was fired. Several old cast-iron guns bored on this system burst in the Crimean War from the projectile wedging in the gun. In 1855 Armstrong experimented with a breech-loading rifled gun, firing a lead-coated projectile. The rifling consisted of a large number of shallow grooves having a uniform twist of 1 in 38 calibres. When the gun was fired the lead-coated projectile, which was slightly larger in diameter than the bore of the gun, was forced into the rifling and so gave rotation to the elongated projectile.
Fig. 22.—Sections of Rifling.
Whitworth in 1857 brought out his hexagonal bore method of rifling and a projectile which was a good mechanical fit to the bore. Good results were obtained,
