Angstadt Arms Bolt Carrier Group, Black, .223/556 AA56BCGNIT 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 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.