Bolt Carrier Group for AR-15. Made from Mil-Spec Carpenter 158 steel. Bolt is shot peened, high pressure tested and magnetic particle inspected. Gas key is machined from bar stock, chrome lined phosphate coated, and secured with grade 8 fasteners and staked per mil-spec. Bolt carrier is phosphated outside and chrome lined inside. For packaging, the BCG ships dry and will darken to black with CLP or other lubricant.