Machine Gun Feeding: Belt System

For sheer volume of ammunition, the belt system is usually the best option. Ammunition belts consist of a long string of cartridges fastened together with pieces of canvas or, more often, attached by small metal links. Guns that use this sort of ammo have a feed mechanism driven by the recoil motion of the bolt. You can see how this sort of mechanism works in the diagram below.

The bolt (1) in this gun has a small cam roller (5) on top of it. As the bolt moves, the cam roller slides back and forth in a long, grooved feed cam piece (2). When the cam roller slides forward, it pushes the feed cam to the right against a return spring (6). When the cam roller slides backward, the spring pushes the cam back to the left. As it moves, the feed cam pivots a feed cam lever from side to side. The feed cam lever is attached to a spring-loaded pawl (8), a curved gripper that rests on top of the ammunition belt. As the cam and lever move, the pawl moves out, grabs onto a cartridge and pulls the belt through the gun. When the bolt moves forward, it pushes the next cartridge into the chamber. You can see how this works in the diagram below.

The feed system drives the ammunition belt through cartridge guides (2) just above the breech. As the bolt slides forward, the top of it pushes on the next cartridge in line. This drives the cartridge out of the belt, against the chambering ramp (3). The chambering ramp forces the cartridge down in front of the bolt. The bolt has a small extractor, which grips the base of the cartridge shell when the cartridge slides into place. As the cartridge slides in front of the bolt, it depresses the spring-loaded ejector (6).

When the firing pin hits the primer, propelling the bullet down the barrel, the explosive force drives the operating rod and attached bolt backward. The extractor pulls the spent shell out of the breech. As the bolt keeps moving backward, the spring-loaded ejector pushes on the base of the shell. When the shell clears the chamber wall, the ejector springs forward, popping the shell out of the gun through the ejection port.

This system lets you fire continuously without reloading. Theoretically, you could make ammunition belts of any length, so they are a great means of providing a constant supply of ammunition. The problem is that the belt is fairly cumbersome, and there's a relatively high likelihood of the feed mechanism jamming.

The Vickers MK1 belt-fed machine gun, a favorite of the British military, played a crucial role in World War I and World War II. The gun is cooled with a special water-filled jacket. As the water boils, the steam flows out to a collection can, where it condenses back into a liquid for re-use.

Photo courtesy Department of Defense Heavier machine guns, such as this .50-caliber M-2, may be mounted on tanks, jeeps, boats and helicopters.

Gun manufacturers are continually adding new modifications to machine guns, but the basic mechanism has remained the same for more than a hundred years. Whether or not you've ever held a machine gun, or even seen one, this device has had a profound effect on your life. Machine guns have had a hand in dissolving nations, repressing revolutions, overthrowing governments and ending wars. In no uncertain terms, the machine gun is one of the most important military developments in the history of man.

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