The heart of a reliable AR-15 build is a quality 5.56 bolt carrier group assembly. These are the same high quality BCG’s that angstadt makes for law enforcement and military groups around the world. Machined to mil-spec dimensions and finished in a beautiful black nitride finish, this bolt will continue to run and looks great doing so. The durability and reliability of these is due to the 8620 alloy steel carrier, and carpenter 158 tool steel bolt. These are M16 cut/full auto capable.