Our upgraded nickel boron bolt carrier group is an eye catching addition to your AR build. Mil-spec dimensions and coating ensure the highest quality and correct component interface. Features: Machined from 8620 Tool Steel (Carrier) and 9310 Steel (Bolt) Carrier has forward assist serrations Shrouded firing pin Nickel Boron Coating inside and out (Bolt, Carrier, and Gas Key) Forged Mil-Spec gas key attached with Grade 8 hardware and Properly staked. 5.56 Bolt is shot Peened and MPI Mil-Spec Extractor Spring, black extractor insert, Viton O-Ring Tool Steel Extractor High quality BCG