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.Complete Phosphate M-16 BCGPhosphate and Nickel Boron Coating Inside and Out (Bolt, Carrier, and Gas Key)Laser Engraved with ST Spider logoMil Spec Carrier 8620 Tool Steel Full Auto M-16Mil Spec Bolt 158 Carpenter Steel or 9310 Depending on Supply Shot Peened High Pressure Tested (HPT) Magnetic Particle Inspected (MPI)Mil Spec Extractor 8620 Tool Steel Nickel Boron Finish Extractor Spring Black Extractor Insert Viton O-RingMil Spec Gas Key 8620 Tool Steel Grade 8 Hardware Properly Staked Firing Pin with Hard Chrome Finish Cam Pin Phosphate and Nickel Boron Finish Retaining Pin Weight: 11.6oz