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246
MACHINE-GUN


carrier and cartridge on it consequently rising a little and falling again (this latter action is incidental only to the form of the parts, and is not a necessity). The retracting springs now react and pull the slide forwards; the cam (98) strikes the dog (23), which, as the spring arrangement is of the “ non-return " class, does not yield but is depressed, and the

FIG. 20.-Hotchkiss Gun mounted. front of the carrier and the cartridge on it are therefore raised sharply, and the latter placed in the path of the bolt. The bolt being now pulled forwards, the cartridge is driven off the carrier into the breech, and the bolt locked by the pin (14), causing the bolt to drop in 'front of the recoil blocks; the carrier is pushed down fiat by the advance of the cam lug (98), the trip releases the sear (Io), and the projection (96) pushes back the feed lever, completing the action of feeding a fresh cartridge forward. The position shown in fig. 17 is now resumed. It is clear that were the trigger kept permanently pulled the gun would fire immediately the bolt was locked and the sear (10) depressed, and the action would become automatic. The object of two detents. though now probably obvious, may here be explained. The whole action of the gun depends upon the hammer after it is pushed back by the bolt being held back until the bolt has gone completely forwards and locked the breech. If only the trigger detent existed, and that were kept pressed down, the hammer, alter being pushed back by the bolt, would immediately ifollow up the latter, and might fire the cartridge prematurely, or fai to fire it at all; hence the use of the sear in addition to the trigger. To cock the lock, or work the mechanism by hand, the gas lever is pulled round by the pin (30) provided for the purpose, and by this means the gun is prepared for firing. A brass tongue on the end of the belt is pushed through the opening above the feed-wheel and then pulled from the other side of the gun as far as it will go. This places a cartridge in front of the extractor, and if the gas lever be now pulled right back and let go, this cartridge is placed in the breech as already described, and the gun is ready for firing. If it be desired to remove a belt from the feed, a button (68) is pressed and the feed-wheel is then free to revolve backwards. The gun is sighted with the ordinary rifle-pattern sights, up to 2000 yds. or more if required. It weighs about 40 lb, and can fire about 400 rounds per minute as usually adjusted, though this rate can be increased. There is no means of altering the gas pressure in the field as with the Hotchkiss. {The diagrams have been made from drawings, by permission of the Colt Arms C0mpany.] Comparing the principle of employing a recoiling barrel with that of using a portion of the gas, the advantages of the former are that the recoil is made to do useful work instead of straining the gun and mounting in its absorption; the latter system, however, has undoubtedly the advantage in simplicity of mechanism (the Hotchkiss is extraordinarily simple in construction for an automatic gun), and in the large margin of power for working the mechanism with certainty in all conditions of exposure to climate, dust, and dirt. While inferior in this respect, it is nevertheless the fact that the Maxim has proved itself in the held even in savage warfare in the roughest country to be a very efficient and powerful weapon. The great difficulty which has to be met in all single-barrel machine guns is the heating of the barrel. The 7% pints of Water in the water-jacket of the Maxim gun are raised to boiling point by 600 rounds of rapid fire-i.e. in about 1% minute sand if firing be continued, about 1% pints of water are evaporated for every 1000 rounds. Assuming that the operation is continuous, the rate of waste of energy due to heat expended on the water alone is equivalent to about 20 horse-power (294 foot tons per minute). The water-jacket acts well in keeping down the temperature of the barrel; but apart from the complications

FIG. 21.-Tripod mounting (Mark IV.), for Brh:isliTlExim. entailed by its use, the provision of water for this purpose is at times exceedingly troublesome on service. In the Hotchkiss and Colt guns, which have no water-jacket, an attempt is made to meet the heating, in the one by the radiator, and in the other by a very heavy barrel. One of the. most modern types of gun is the Schwarzlose, which is manufactured at Steyr in Austria, and was adopted by the Austrian army in 1907. This weapon is remarkable for its simplicity. There are only IO main working parts, and any of these can be replaced ina few seconds. It is operated by the gases of the explosion, has a water-jacket that allows 3000 rounds to be fired without rehlling. The “life ” of the gun barrel is stated to be 35,000 rounds without serious loss of accuracy. The weight 'of the gun is 37'9 lb. It is a belt loader. The Italian Perino gun, adopted in 1907, is a recoil-operated weapon, and is loaded by a metal clip. The Skoda gun, some of which type are used in ]apan and China, is loaded by a hopper feed, and is gas-operated. The Bergmann gun is a belt loader, but the belt passes down a “ gravity feed ” an arrangement which saves a number of working parts. One defect common to all is that it is by no means easy to proportion the fire to the target, as there are only two rates of fire, viz. rapid automatic and slow single shots. To Ere a single shot requires practice, since thegun will fire some 7 shots