This FailZero Full Auto Rated Lightweight (Low Mass) Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most mil spec AR15 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. Full Auto Rated 9.6 oz. Total 5.56/.223/300 Blackout Compatible Nickel Boron treated Extreme durability Dry lubricity Corrosion resistant