FYI
Any weapon capable of continuous fire, with or without a single-shot option, is an automatic weapon. A machine gun is an automatic weapon, but not all automatic weapons are machine guns. A machine gun, as the term is used in and by the military, and an assault rifle (the military really doesn't use either this term or "assault weapon") are two very different things. A machine gun is a weapon that is capable of very high rates of fire due to the fact that it is fed by belted ammunition. It may be capable of firing in a single-shot mode, but continuous fire (practically speaking, repeated 4-6 round bursts) is the default. An assault rifle's default mode is single-shot, aimed fire. Neither the current version of the M-16 rifle (the M-16A2) nor the more recent M-4 carbine has an automatic fire mode, although they do have a 3-shot alternative to the single-shot. The M-4A1 can fire automatically. Although their cyclic rate of fire is close to that of a machine gun (and greater than that of the venerable M-2 .50 cal machine gun), the actual, sustained, rate is much lower because of the need to replace the magazine every 30 shots.