This is a standard full-auto M16 cut bolt carrier group. It is designed to function with the Echo AR-II and the Echo Sport. Bolt Assembly Bolt: Shot Peened; Magnetic Particle Inspected and Marked Bolt Material: 9310 Alloy Steel Compatibility: .223 / 5,56 / 300BLK Extractor: Shot Peened Hardened Tool Steel Extractor O-Ring: Viton, Mil-Spec Gas Rings (3): Mil-Spec Finish: BLACK NITRIDE Bolt Carrier Material: 8620 Steel Design: Heavy Profile M16 Style (Preferred for most AR-15 Builds) Gas Key Screws: Grade 8; Properly Torqued and Staked to Mil-Spec Gas Key Material: 4130 Steel Finish: BLACK NITRIDE Cam Pin Material: 4140 Steel Finish: BLACK NITRIDE Firing Pin Material: 8740 Steel; Centerless Ground; Hard Chrome Plated Weight: 11.6 Ounces 100% USA Made