Your bolt carrier group is one of the most critical parts of your build. Don't buy an imitation. This is the same BCG we use on our builds. Features: Complete phosphate M-16 BCG Phosphate coating inside and out (bolt, carrier, and gas key) Laser engraved with ST Spider logo Mil-Spec carrier - 8620 tool steel, full auto M-16 Bolt- 158 carpenter steel, shot peened, high pressure tested (HPT), magnetic particle inspected (MPI) Mil-Spec extractor - 8620 tool steel, phosphate finish, extractor spring, black extractor inser and Viton O-ring Mil-Spec gas key - 8620 tool steel, grade 8 hardware, properly staked, chrome interior Firing pin with hard chrome finish Cam pin phosphate finish Retaining pin