ok. so to wrap it up ar15 machined out=bad news. Ar15 with auto sear selector swith and all other M16 parts=bad news. But if you possess just an M16 lower receiver with semi auto parts (ar15) they will still drop the hammer on you?
Yes. It is all in the numbers.
Then again can you think of the last time anyone looked at a serial number on any gun you own?