Yes, they are. You need to knock them out from left to right, and replace them from right to left. The holes in the left side of the receiver have a metal insert of some kind that locks the pin in.Looks like in USC lower the trigger group is held in with 4 pins and the trigger group will come out in piecs.
Is this correct.
Found one in a candle up on top of the DVD shelf last time I took one apart... lolAnd if you take it apart, watch out for the springs around the rearmost pin. They will fly across the room and it will take you an hour to find them at 2am because they are buried inside a houseplant. (ask me how I know.) :90: