FailZero AR9, 9MM BCG, Black Nitride FZ-9MM-NITRIDE-BCG This 9mm Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most 9mm AR platform rifles and pistols. The FailZero Black Nitride 9mm BCG is compatible with both lowers designated for Glock or Colt magazines. All critical parts are coated with Salt Bath Nitride (Black) which provides durability and increases both wear and corrosion resistance.