The heart of a reliable AR-15 build is a quality 5.56 bolt carrier group assembly. These are the same high quality BCGs 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.Features :Machined from 8620 alloy steel5.56 Bolt is machined from Carpenter 158 tool steelHigh pressure tested