Guardians of the Stars
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 several hundred rounds per minute.
Fully automatic weapons are generally categorized as submachine guns, machine guns, or autocannons. A machine gun is often portable to a certain degree, but is generally used when attached to a mount or fired from the ground on a bipod, and generally fires a rifle cartridge 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. 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.
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 (SAW) are a variation of light machine gun and require only 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.
Machineguns also includes gatling style weapons such as the minigun. Having multiple barrels allows for a high rate of fire while operating cooler than single barreled designs.