The term "assault weapon" in and of itself is as ridiculous as it is redundant.
It is like saying "vehicle tire", "cutting knife", or "writing pen". By definition the purpose of a "weapon" is to "assault" - whether the reason is offense or defense the action it achieves is to assault.
Some things, lets say a shotgun, can be used as a hunting tool - in which case it is not primarily used as a weapon. Although most shotguns could be used as a club, that is to say as a weapon, to assault somebody.
The term is nonsensical.