12 to 15 years ago I purchase an undedicated AR-15 lower receiver that the FFL seller made into a dedicated pistol in .223 by marking it as such on the 4473.
I want to put a 10.5” 300BLK upper on it. Is there any prohibition in doing that?
I want to put a 10.5” 300BLK upper on it. Is there any prohibition in doing that?