Bolt Carrier: 8620 Steel Case Hardened Machined from Billet Firing Pin: 17-4 H-900 Steel Center-less Ground Gas Key: 4140 Steel with Grade 8 Screws Properly Staked Machined from Billet Cam Pin: 4140 Hardened Steel Finish: Black Nitride finished with an ultra-hard corrosion-resistant top surface layer for wear resistance and minimal need for lubricants. Bolt: 9130 steel Shot Peened Mil-Spec Dimensions CNC Ground After Heat Treat Black Nitride Finished MPI/HPT Extractor: 4140 Billet Manganese Phosphate Finished for Positive Grip