I quibble with characterizing weapons as dangerous. Absent a legal definition of "dangerous" to the contrary, I characterize things as dangerous as those things that are unpredictable in their operation. My AR's are dead-on reliable, because they are absolutely predictable in their operation. OTOH, a lion is dangerous because one day you put your head in its mouth and you're fine, the next day, not so much. Same action, random outcome.It is "dangerous AND unusual", not "dangerous OR unusual". Thus the "common use test".
All weapons are dangerous, or they wouldn't be weapons. AR-15's are NOT unusual.
Something that works fine one moment and wrong the next is dangerous, it is unpredictable outcomes that are dangerous because despite providing the same inputs you don't know what outcome you shall receive.