Doublestar Corp. Bolt Carrier Group, Chrome Lined, Includes O Ring AR100 This 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. Includes bolt assembly" firing pin" firing pin retaining pin" cam pin and complete carrier.