This 9mm AR Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most 9mm AR platform rifles and pistols. The FailZero 9mm BCG is compatible with both lowers designated for Glock or Colt magazines. All critical parts are coated with EXO Nickel Boron technology that provides permanent dry lubricity, extreme durability and increases both wear and corrosion resistance. Our patented Nickel Boron coating will reduce friction and improve the overall performance of your rifle.