A machine gun (MG) is a fully automatic, rifled auto-loading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles are typically designed more for firing short bursts rather than continuous firepower and are not considered true machine guns. Submachine guns fire handgun cartridges rather than rifle cartridges, therefore they are not considered machine guns, while automatic firearms of 20 mm (0.79 in) caliber or more are classified as autocannons rather than machine guns.
Top: IWI Negev Bottom: FN MAG (general purpose machine gun)
Czechoslovak 7.62 mm Universal Machine gun Model 1959
A .50 caliber M2 machine gun: John Browning's design has been one of the longest-serving and most successful machine gun designs
A vehicle with a Sumitomo M2 heavy machine gun mounted at the rear
An automatic firearm or fully automatic firearm is an autoloading firearm that continuously chambers and fires rounds when the trigger mechanism is actuated. The action of an automatic firearm is capable of harvesting the excess energy released from a previous discharge to feed a new ammunition round into the chamber, and then igniting the propellant and discharging the projectile by delivering a hammer or striker impact on the primer.
A M2 Browning machine gun, surrounded by ejected cartridge cases
A United States Army soldier laying automatic suppressive fire with an M60 machine gun during the Vietnam War