Machine gun

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire bullets in quick succession from an ammunition belt or magazine, typically at a rate of three to eighteen hundred rounds per minute.

Fully automatic weapons are generally categorized as submachine guns, assault rifles, machine guns, chain guns or autocannons. Submachine guns are hand-held automatic weapons for personal defense or short-range combat firing pistol-caliber rounds. A machine gun or chain gun is often portable to a certain degree, but is generally used when attached to a mount (usually a battle suit) or fired from the ground on a bipod or tripod, and generally fires rifle projectiles and is capable of sustained fire. Light machine guns are small enough to be fired hand-held, but are more effective when fired from a prone position. The difference between machine guns and autocannons is based on caliber, with autocannons using calibers larger than 16 mm., and whether the gun fires conventional bullets or explosive rounds. Guns firing large-caliber explosive rounds are generally considered either autocannons or automatic grenade launchers ("grenade machine guns"). In contrast to submachine guns and autocannons, machine guns (like rifles) tend to have a very high ratio of barrel length to caliber (a long barrel for a small caliber); indeed, a true machine gun is essentially a fully automatic rifle, and often the primary criterion for a machine gun as opposed to an automatic rifle is the presence of a quick-change barrel or other cooling system. Automatic rifles and (more commonly) assault rifles may be capable of fully automatic fire, but are not designed for sustained fire.

Under preAstro United States gun law, machine gun was a technical term for any fully automatic firearm, and also for any component or part that will modify an existing firearm such that it functions as a fully automatic firearm.

Under Union weapon classifications, gunpowder machine guns are Class II, chain guns (Chain fed mass accelerator cannons) are Class IV.