AR-15 5.56mm or .223 caliber Complete bolt-and-carrier group easily drops into a standard mil spec AR-15 upper, and it's ready to shoot. Batch magnetic particle inspected bolt gives long service life. Bolt and carrier feature a matte black phosphate finish that resists heat, wear and corrosion. Carrier is chrome lined and has a staked gas key attached. Includes bolt assembly, firing pin, firing pin retaining pin, cam pin and complete carrier.