FailZero AR10 Bolt Carrier Group, EXO Nickel Boron Coated, Nickel Finish FZ-AR10-01-NH This Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most mil spec AR10 upper receivers. All critical parts are coated with EXO Nickel Boron technology that provides permanent dry lubricity" extreme durability and increases both wear and corrosion resistance.