The nature of a weapon lies in it's
application, i.e. a
pistol is nice for "home security", but you can't exactly mount a bloody assault into a enemy camp with a
9mm. In the military sense, the word "assault" is somewhat similar to "offensive", i.e. assault weapons are weapons best used for
just that.
M-16's are the hallmark of american assault weaponary because of their
versatility, although they can't hold a candle to an
AK-47 in terms of
durability. Any weapon can be used to assault someone, per se. But you need a special kind of weapon to mount a full-scale assault, just like how you need a special kind of soldier to save the president's daughter,
Rambo!
Effective assault weaponary lies in it's, as earlier stated, versatility in the face of diverse situations, i.e. an M-16, if used properly, can drop a mark at 1 klick (see:
kilometer), as well as shower bodies at close range with hot lead. A
pistol? 20 meters, if you're a good shot, although this varys from make and model. A
shotgun? 4 meters will give you a loose spread pattern unless you're firing
slugs. The two previous weapons don't have widespread military use, (the pistol being the exception with officers) because they aren't very
versatile. Sub-machineguns are neat if you're a
terrorist, or involved in any close-quarters urban combat. But they just aren't all that
practical in a military setting. You need
assault weapons!