Introduction to Machine Gun

Machine Gun, a weapon loaded and fired automatically, designed to discharge a long-continued stream of projectiles of rifle caliber or slightly larger than rifle caliber. A machine gun is usually belt-fed, with cartridges attached to a belt and automatically fed into the breech. Most belts are of the disintegrating metal-link type in which the links making up the belt come apart upon firing. A few machine guns are magazinefed. (A magazine is a metallic container that brings one cartridge after another into loading position.)

A machine gun is similar to both an automatic rifle and an automatic cannon (used against aircraft). An automatic rifle, however, is lighter and, when firing in the automatic mode, less accurate; an automatic cannon fires a larger-diameter projectile, containing an explosive charge. The machine gun is one of the principal weapons of the infantry. It is a specialty weapon, meaning that relatively few troops in a unit are normally armed with it. The machine gun is also used on tanks and other military vehicles, helicopters, and slow-moving airplanes. The weapon once was commonly used as an antiaircraft gun and as armament for jet fighters and bombers, but it has been superseded for these purposes by automatic cannon.

Most machine guns are air-cooled, usually having aluminum fins or a perforated jacket to radiate heat from the barrel and set up currents of air to aid in cooling. Barrels quickly overheat in continuous fire and are therefore designed to be easily replaceable. Some machine guns, now largely obsolete, are water-cooled, having the barrel surrounded by a tubular jacket containing water.

Most machine guns are capable of firing at a rate of 450 to 700 rounds a minute; some have much higher rates. Because of the danger of overheating the weapon, the gunner does not actually fire this number of rounds within one minute. Machine guns are normally fired in short bursts.

How A Machine Gun Works

Machine guns and other automatic weapons are described as recoil-operated or gas-operated. In a recoil-operated gun the force of recoil when a shot is fired moves the barrel backward a short distance. This movement actuates mechanisms that eject the empty shell casing, load a new cartridge into the chamber, and cock the gun. In a gas-operated gun a part of the gas from discharge of the explosive is led off through a port (hole) in the barrel into a cylinder. There the gas drives back a piston that actuates the ejection, reloading, and cocking mechanisms.

In all machine guns, firing and reloading are continuous as long as the trigger is held back. When the gunner releases the trigger a catch engages the lock or other mechanism at the completion of reloading and cocking, leaving the gun in firing position.

Types of Machine Guns

Machine guns are classed as light, medium, or heavy. Both light and medium machine guns shoot a rifle-sized round.

A Light Machine Gun

is usually equipped with a shoulder stock and normally has a bipod at the end of the barrel. Some light machine guns are adaptable for mounting on a tripod. A light machine gun is operated by one man. From World War I to the early 1960's the principal American light machine gun was the Browning Automatic Rifle (BAR). (The BAR, despite its name, was a light machine gun.) In 1964 the United States adopted the M-16, a true automatic rifle, and the BAR was retired.

In 1984, the United States began equipping its forces with a new light machine gun, the M-249, or squad automatic weapon (SAW). It uses 5.56-mm ammunition.

The submachine gun, or burp gun, is sometimes classified as a special type of light machine gun even though it lacks the accuracy of a true machine gun. It uses pistol-type ammunition.

A Medium Machine Gun

is nearly always used as a crew weapon, operated by a gunner and assistant. It may be fired from a tripod or swivel mount and some models are also equipped with built-in bipods. Examples are the .30 caliber water-cooled Browning Machine Gun (now obsolete), the .30 caliber air-cooled Browning (once an infantry weapon but now sometimes used on vehicles), the 7.62-mm (.308 caliber) M-60, and the 7.62-mm (.308 caliber) M-240, the standard infantry medium machine gun of the U.S. Marine Corps since 1995.

The M-240 can fire as many as 950 rounds per minute with an effective range of 1.1 miles (1.8 km). The U.S. Army uses a version of the M-40 as a mounted gun on tanks and other armored vehicles.

The most devastating United States machine gun is the minigun, developed in the mid-1960's. It is capable of firing from 4,000 to 6,000 rounds per minute. The gun has six barrels arranged in a cylinder that rotates, providing fire through each barrel one after another. The gun uses 7.62-mm ammunition. Miniguns are placed on helicopters and slow-moving airplanes for use against enemy ground troops.

A Heavy Machine Gun

is one whose caliber is between that of a rifle and a cannon. The standard American heavy machine gun is the air-cooled .50 caliber Browning. It is generally mounted on tanks or armored personnel carriers; during World War II it was also used on aircraft. United States infantry troops in stationary defensive positions sometimes use the quad-50, a battery of four .50 caliber Brownings whose effect is much like that of light artillery. The United States Mark 19 Model 3.40-mm heavy machine gun is not a true machine gun but an automatic grenade launcher.

History of Machine Guns

The machine gun had its origin in the long search for rapid-fire firearms. Many multiple-barrel ideas were tried out, the first successful one being the invention of Dr. Richard J. Gatling in 1862. The Gatling gun had 5 to 10 barrels arranged in a cylinder revolved by turning a hand crank. It was made in calibers from .42 to one inch (10.67-25.40 mm) and attained a rate of fire of 1,000 shots a minute. It had occasional use in the Civil War and Indian wars and was used effectively in the Spanish-American War.

The French mitrailleuse was an effective multibarrel gun in the Franco-Prussian War, 1870-71. Sir Hiram Maxim invented the first true machine gun in 1884. It was recoil-operated, water-cooled, and belt-fed. B. B. Hotchkiss invented a revolving cannon patented in 1887.

In the Spanish-American War, the United States used the Colt machine gun, developed by John M. Browning, and the Gatling. The most successful early light machine gun was the Lewis, invented in 1911 by Colonel Isaac N. Lewis of the U.S. Army. The Lewis was used by the British in both World Wars. Machine guns developed by Browning during World War I remained standard weapons for many years.

Machine guns were mounted on airplanes early in World War I. A major problem was how to fire forward without hitting the propeller. This was solved in 1915 by the Germans, who developed the synchronized machine gun; its firing was controlled by the engine crankshaft.

Throughout World War II, machine guns served as a valuable armament for infantry, tanks, ships, and airplanes. During the Korean War, the machine gun was replaced on airplanes by 20-mm and 30-mm automatic cannon. In addition, air-to-air missiles increasingly came into use as the principal weapon in aerial combat. After the Korean War, the machine gun continued to prove valuable and found a new use on helicopters in counterinsurgency warfare.