Automatic Rifle. The major difference between an automatic rifle and a machine gun is the latter is designed for sustained automatic fire. Machine guns will t

Automatic Rifle. The major difference between an automatic rifle and a machine gun is the latter is designed for sustained automatic fire. Machine guns will typically be quite a bit heavier since that helps with sustained fire. Submachine guns are automatic pistols, which is to say they fire lower power pistol ammunition, and, like pistols, usually have shorter barrels than rifles. Typically also have accuracy comparable to pistols rather than rifles.