I was apparently sent an M4E1 upper receiver instead of their regular AR-15 ones. (Score!) Seems good, but I noticed that the forward assist does not have a roll pin. It's a threaded bolt. Anyone else use these uppers or have problems with these little bolts? I'm wondering what the shear strength of these are. I emailed AP, but I have a feeling they probably didn't delve into that when designing it. Could be wrong though.