Machine gun

A machine gun is a fully automatic firearm that is capable of firing bullets in rapid succession. Such automatic weapons with a caliber of 20 mm or larger are generally referred to as autocannons.

Overview

Unlike semi-automatic firearms, which require one trigger pull per bullet fired, a machine gun is designed to fire bullets as long as the trigger is held down and ammunition is fed into the weapon. Although the term "machine gun" is often used to describe all fully-automatic weapons, in military usage the term is restricted to weapons designed to provide suppressive fire in continuous or frequent bursts of automatic fire for as long as ammunition lasts (however, a fully automatic firearm with a projectile caliber of equal to or greater than 20 mm (0.8 inch) is called an automatic cannon).

Related Topics:
Semi-automatic firearm - Trigger - Suppressive fire - Caliber - Inch - Automatic cannon

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Some machine guns have in practice maintained suppressive fire almost continuously for hours; other automatic weapons will eventually overheat, usually in less than a minute. Because they become very hot in operation, practically all machine guns fire from an open bolt, to permit air cooling from the breech between bursts. They also have either a barrel cooling system or removable barrels (so that a hot barrel can be swapped for a cool one.)

Related Topics:
Open bolt - Breech

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Although subdivided into "light", "medium", "heavy" or "general purpose", even the lightest machine guns tend to be substantially larger and heavier than other automatic weapons. Squad automatic weapons (SAWs) are a variation of light machine guns and only require one operator (sometimes with an assistant to carry ammunition). Medium and heavy machine guns are either mounted on a tripod or on a vehicle; when carried on foot, the machine gun and associated equipment (tripod, ammunition, spare barrels) require additional crew members.

Related Topics:
Squad automatic weapon - Light machine gun - Tripod

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The majority of machine guns are belt-fed, although some light machine guns are fed from drum or box magazines, and some vehicle-mounted machine guns are hopper-fed.

Related Topics:
Belt - Magazines

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Other automatic weapons are subdivided into several categories based on the size of the bullet used, and whether the cartridge is fired from a positively locked closed bolt, or a non-positively locked open bolt. Fully automatic firearms using pistol-caliber ammunition are called machine pistols or submachine guns (largely on the basis of size); selective-fire rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles, while those using a reduced-power rifle cartridge are called assault rifles.

Related Topics:
Cartridge - Closed bolt - Open bolt - Machine pistol - Submachine gun - Selective-fire - Automatic rifle - Assault rifle

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The machine gun's primary role in ground combat is to provide suppressive fire on an opposing force's position, forcing the enemy to take cover and reducing the effectiveness of his fire. This either halts an enemy attack or allows friendly forces to attack enemy positions with less risk.

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To this end, most light machine guns and general purpose machine guns are not designed for high accuracy, as would be expected of a rifle. Most are designed with a small degree of inaccuracy, referred to as the "cone of fire", because the rounds spread out as they travel towards the target area. Light machine guns usually have simple iron sights. A common aiming system is to alternate solid ("ball") rounds and tracer ammunition rounds (usually one tracer round for every four ball rounds), so shooters can walk the fire into the target and direct the fire of other soldiers.

Related Topics:
Light machine gun - General purpose machine gun - Rifle - Tracer ammunition - Soldier

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Assault rifles are a compromise between the pistol-caliber submachine gun and a traditional rifle firing a full-power cartridge, allowing single-shot, burst and full-automatic fire options.

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Many heavy machine guns, such as the M2 .50 caliber machine gun, are accurate enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the record for a long-distance shot at 7382 ft (2250 m) with a .50 caliber heavy machine gun he had equipped with a telescopic sight. This led to the introduction of .50 caliber anti-material sniper rifles, such as the Barrett M82.

Related Topics:
Heavy machine gun - M2 - Vietnam War - Carlos Hathcock - Telescopic sight - Sniper rifle - Barrett M82

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