Assembled Bolt Carrier Group for AR-15/M16 8620 M16 style carrier Black Nitride finish Properly heat treated Final grind before plating 9310 Steel 5.56/.223 bolt Shot peened MPI – Magnetic Particle Inspected 4140 Gas Key -Black Nitride finish -Properly torqued with Grade 8 fasteners -Properly staked to ensure reliability 4140 Cam Pin -Heat Treated -Black Nitride finish Machined from solid 4140 bar stock, heat treated and shot peened Phosphate coated for reliable extraction Extractor insert included O-Ring included Firing pin precision machined from 17-4 H-900 Stainless Steel100% USA MadeMidwest Industries Limited Lifetime Warranty