Machine gun is an automatic weapon that can fire from 400 to 1,600 rounds of ammunition each minute. Machine gun barrels range in size from .22 caliber to 20 millimeters. Ammunition is fed into the gun from a cloth or metal belt, or from a cartridge holder called a magazine. Because machine guns fire so rapidly, they must be cooled by air. Machine guns are heavy weapons and are usually mounted on a support.
Operation.
In all machine guns, extremely high gas pressure provides the operating energy for the firing cycle. The cycle begins when the propellant charge in the cartridge case burns. This combustion creates the gas pressure that is used in the blowback, gas, and recoil operating systems. All three systems fire the projectile through the bore of the barrel, eject the cartridge case, place a new cartridge in the firing chamber, and ready the mechanism to repeat the cycle.
In the blowback system, the operating energy comes from the cartridge case as the case is forced to the rear by the gas pressure. The case moves against the bolt (a device that opens and closes the bore), driving the bolt backward against a spring. The case is ejected, and the compressed spring drives the bolt forward. As the bolt moves forward, it cocks the firing mechanism, picks up a new cartridge, carries it into the chamber, and the cycle begins again.
In the gas system, the gas pressure drives a piston against the bolt. The bolt is driven to the rear, providing energy for a cycle like that of the blowback system.
In the recoil system, the bolt locks to the barrel when the gun is fired. These parts remain locked together as they are forced to the rear by the gas pressure. This movement provides energy to operate the gun.
Ground weapons.
The 7.62-millimeter M60 machine gun is a major infantry weapon. It is air-cooled and gas-operated, and fires about 600 rounds a minute. The M60 replaced the Browning machine gun, an important weapon in World Wars I and II, and the Korean War.
Aircraft weapons.
By the close of World War I, several types of machine guns were mounted on airplanes. These types included the Vickers, Maxim, Hotchkiss, Colt-Martin, and Lewis. Some machine guns were synchronized to fire in between the blades of propellers.
During World War II, fighters and bombers carried machine guns as armament. They also carried automatic cannon up to 20 millimeters in size. During the Vietnam War, airplanes and helicopters called gunships carried machine guns or cannon. Today, most fighter planes and gunships carry rockets for air-to-air and air-to-ground use. Bombers use machine guns mounted in groups of two or four in power-driven turrets. The Vulcan 20-millimeter aircraft cannon has six rotating barrels. It can fire more than a ton of metal and explosives each minute.
Antiaircraft weapons.
The .50-caliber Browning machine gun was used as an antiaircraft weapon during World War II. It was used alone, or in groups of two or four. Large-caliber automatic cannon that fired explosive shells were also developed as antiaircraft weapons. The 20-millimeter, Swiss-made Oerlikon gun was used on U.S. Navy ships. It was a self-fed, self-firing cannon that could fire 600 rounds a minute.
History.
A type of machine gun appeared as early as the 1500’s. It consisted of several guns bound together in a bundle or spread out in a row. A device that was fitted to the gun barrels caused them to fire simultaneously or in series. But little success was achieved until the Civil War, when many quick-fire guns appeared. Practical, rapid-fire, mechanical guns were used in the Franco-Prussian War, when soldiers operated them with a crank or lever. The French Montigny mitrailleuse and the American Gatling were among the more successful of these guns.
In 1883, Hiram Maxim, an American-born inventor, developed the first entirely automatic machine gun to gain wide acceptance. By the time of World War I, many different types of machine guns had come into use.
