Comment by pandaman

Probably some local law? There are 50 states and much more cities, every one of them can have an "Assault Weapon" legislation with whatever definition they want, starting from the color and ending with the "shoulder thing that goes up".

Also, barrel length is one of the most common theme in firearms bans. Usually those consist of legal limits on the minimum barrel length in an effort to prevent people from concealing it, I guess.