Page:EB1922 - Volume 31.djvu/861

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mount is placed in its lowest position, so that it forms a litter with the front and rear legs projecting for handles ; or the front legs may be hinged back to the rear, when the mount becomes a sledge which may be dragged by means of cords hooked into rings provided for this purpose.

FIG. 4. Vickcrs Machine-Gun.

Transportation of Machine-Guns. The standard method of transporting machine-guns and their equipment is by means of animal-drawn transportation. For this purpose the British use limbered wagons drawn by horses. The French use small carts or voiturettes, which are drawn by one horse or dragged by men. Before the VVorld War, pack outfits were the only transportation used for machine-guns by the United States. During the World War, the one-mule cart, patterned after the French design, became standard for the transportation of both machine-guns and their ammunition, though motor transportation was provided in the case of special machine-gun battalions.

The Vickers Machine-Gun. The Vickers machine-gun is a Maxim greatly lightened, and slightly changed as to details of the mecha- nism. The description of the operation of the Maxim will serve equally for the Vickers. The weight of the gun is 38 lb., including 7! pt. of water in the jacket. The ammunition belt used is the same as for the Maxim. When the gun is used in aircraft, metallic link belts are employed.

FIG. 5. Browning Machine-Gun.

The Browning Machine-Gun. In this gun, as in the Vickers, the actuating force is the recoil of the barrel. The principal parts in the mechanism are the barrel, which is mounted in a water-jacket and arranged to have a sliding motion; a heavy rectangular breech- block, or bolt; a strong piece screwed on to the barrel, called the barrel extension, on which the bolt slides; a vertical lock in the barrel extension, for locking the bolt against the rearward thrust of the explosion; a short curved lever, called the accelerator, for utilizing the recoiling energy of the barrel for throwing the bolt rapidly to the rear; a firing pin and trigger mechanism; a belt- feeding mechanism ; and the necessary springs and small parts. The parts are enclosed in a rectangular breech casing consisting of side, top, and bottom plates riveted together, with a hinged cover and a sliding back plate. The relations of these parts in both the forward and rearward positions can be seen in the illustration. When the trigger is pulled, its forward end draws the sear downward, thus releasing the firing pin, which flies forward and primes the cartridge. The force of the explosion causes the barrel to recoil sharply to the rear, carrying with it the barrel extension and the bolt. During the backward motion, the projecting end of the breech-lock pin strikes against cams on the forward extension of the lock frame. These cams force the breech lock down, thus unlocking the bolt from the

barrel extension. At this instant the rear end of the barrel extension in its backward motion comes into contact with the curved face of the accelerator. The pressure of the barrel extension on the accelera- tor causes it to rotate so that its point, which is in contact with a lip

EXTRACTOR

BACKWARD POSITION TOP PLATE

TRIGGER

BACK PLATE

CARTRIOOE

BARREL

FIRING PIN

FORWARD POSITION \

BOTTOM PLATE

FIG. 6. Browning Machine-Gun.

on the breech block, swings away from the barrel. As the accelerator rolls over, the curve on its face causes the point of contact with the barrel extension to move closer to its pivot, which is the fulcrum of its motion. This produces a rapid acceleration of the motion of the bolt, with a corresponding increase of resistance to the rearward motion of the barrel. The result is that the sharp backward motion of the barrel is checked, and its momentum is transferred to the bolt, which is thrown to the rear of the breech casing. During the backward motion of the bolt the firing pin is cocked by the cocking lever, and a live round is drawn from the belt by the extractor and forced downward into guideways in the face of the bolt by means of a cam in the cover plate which acts on the top of the extractor. After the backward motion of the bolt is completed, the driving spring pushes it forward. During the forward motion of the bolt a cam in its upper surface acts through a lever to feed the be_lt along so that a fresh cartridge is in place. At the same time a spring stud in the side of the extractor engages in a cam groove cut in the side plate. This cam first lowers the extractor, so as to bring the cartridge in line with the chamber. After the cartridge is partly into the chamber, the cam raises the extractor into a position to grasp the fresh cartridge that is in the feedway. Just before the bolt com- pletes its forward motion the lip on its under side strikes the tip of the accelerator and rotates it forward. This motion of the accel- erator, acting through the barrel extension, forces the barrel for- ward. At the end of this movement, the breech lock is carried up the inclined face of the breech-lock cam, which causes the breech lock to rise and engage in its slot in the bolt, thus locking the bolt and barrel extension together. After the locking is completed, the further motion of the bolt brings the inclined faces on the sear into engage- ment with the corresponding surfaces on the trigger; and if the trigger is being held down the action of these surfaces forces the sear down, releasing the firing pin and causing the cycle to be repeated. This gun, when supplied to infantry, uses woven cartridge belts holding 250 rounds each. An excellent feature of this belt is its cheapness and ease of manufacture. It consists simply of a narrow strip of cotton tape with cartridge pockets woven in it. There are no metallic components to make the belt expensive or render its manufacture difficult. A belt-filling machine is furnished for loading cartridges rapidly into the belts. The weight of the Browning machine-gun, with 7 pt. of water in the jacket, is 37 lb. The tripod weighs 45 lb. The rate of fire is about 500 rounds per minute. In the Browning aircraft machine-gun the water-jacket is replaced by a light ventilated barrel casing, and a trigger mechanism capable of being operated by a synchronizing device is substituted for the regular trigger and sear. In order to cause the gun to operate at a higher speed, the breech block is greatly lightened. The gun fires at a speed of about 1,100 shots per minute. This gun uses disintegrating belts formed of metallic links.

The Marlin Aircraft Machine-Gun. This gun is a development of the Colt machine-gun (see 17.244). It is greatly lightened to fit it for use in the air, and a reciprocating piston operating in a gas cylin- der under the barrel is substituted for the swinging gas lever used in the Colt gun. Except for minor changes, the breech action of this gun is the same as that of the Colt. A special firing mechanism and trigger motor is fitted to allow the gun to be fired through the propeller by either a mechanical or a hydraulic synchronizing gear. This gun uses the same disintegrating metallic belt as is furnished for the Browning. The gun weighs 23! lb., and fires at the rate of about 680 shots per minute.

The Lewis Aircraft Machine-Gun. The mechanism of this gun is the same as that of the Lewis machine-rifle, described in the article