FailZero, Bolt Carrier Group, Bolt Carrier Group, Silver, No Hammer, Nickel Boron NEW Nickel Boron Treater Dry Lubricity Extreme Durability Corrosion Resistant Product Description This 6MM ARC Bolt Carrier Group (BCG) comes fully assembled and ready to drop into most Mil-Spec upper receivers chambered in 6MM ARC. All critical parts are coated with EXO Nickel Boron Technology that provides permanent dry lubricity, extreme durability and increases both wear and corrosion resistance.