a type of weapon. machine guns first appeared in world war I and revolutionized warfare, leading to the invention of tanks. machine guns are subdivided into light machine guns and heavy machine guns (the former can be used and carried by a single person while the latter is mounted and has to be used by a crew).
machine guns enabled a single soldier to kill a whole group of other songles in a few seconds.
a specific type of rifle. it is fully automatic, fed by a high-capacity magazine and has a pistol grip. Assault rifles were designed to have the accuracy and power of a rifle, but the automatic fire and portability of a submachine gun. Assault rifles usually use a shortened rifle cartridge, though some do not. such as the Heckler and Koch G3 and FN FAL.
the world's most famous assault rifle is the AK-47. the first assault rifle was the Nazi-made Sturmgewehr 44.