The Noveske Bolt Carrier Group features a full auto carrier with a staked gas key. The bolt is machined from 158 Carpenters Steel. The bolt is then Shot peened and MP tested to ensure years of rugged use without fail. Mil-Spec bolt face works for standard cartridges, such as 5.56mm, 300 Blackout and 22 Nosler. Details: Cartridge: 5.56x45mm NATO Color: Black Phosphate Material: Steel Mil-Spec or Commercial: Mil-Spec Country of Origin: United States of America Compatible With: AR-15 SKU: 496470