Midwest Industries Bolt Carrier Group BCG 9310 5.56/AR15 Black Titanium Nitride Finish. The Carpenter 158 Bolt is heat treated shot peened precision ground for perfect dimensions and MPI Tested. The 4140 Billet Gas Key is properly torqued with Grade 8 fasteners and properly staked to ensure reliability. The 4140 Billet Cam Pin is nitride treated for wear resistance. The Billet Machined Extractor is machined from solid 4140 bar stock heat treated and shot peened coated for reliable extraction extractor insert and O-Ring are included. Specifications for Midwest Industries 5.56/AR15 9310 Bolt Carrier Group (BCG): Manufacturer: Midwest Industries Color: Black Finish: Nitride Fabric/Material: Stainless Steel Carrier Material: 8620 Steel Bolt Material: 9310 Steel Caliber: 5.56mm Gun Make: AR Platform Gun Model: M16 AR-15 Hand: Right Weight: 11.4 oz Country of Origin: USA Gun Type: Rifle Features of Midwest Industries 5.56/AR15 9310 Bolt Carrier Group BCG Assembled Bolt Carrier Group BCG for AR-15/M16 8620 M16 style carrier HM Black Nitride finish Properly heat treated Final grind before plating Carpenter 158 5.56/.223 bolt Heat treated Shot peened Precision ground for perfect dimensions MPI - Magnetic Particle Inspected 4140 Billet Gas Key Properly torqued with Grade 8 fasteners Properly staked to ensure reliability 4140 Cam Pin Heat Treated Billet Machined Extractor 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 Steel Package Contents: Midwest Industries 5.56/AR15 9310 Bolt Carrier Group Extractor Insert O-Ring Included What firearm models does the manufacturer say Midwest Industries 5.56/AR15 9310 Bolt Carrier Group (BCG) is compatible with? The manufacturer says that Midwest Industries 5.56/AR15 9310 Bolt Carrier Group (BCG) is compatible with AR-15 M16Midwest Industries MI-BCG-NIT: Bolt Carrier Group 9310 5.56/AR15 Black Titanium Nitride Finish