Faxon Firearms AR Bolt Complete 5.57 Black. 56/300 Bolt. Faxon Firearms machined these Bolt Carrier Groups from 9310 tool steel with an S7 tool steel extractor for maximum durability. The Faxon Firearms AR-15 5.56/300 Nitrided Bolt is resistant to corrosion keeping the elements at bay to provide several years of use. Upgrade your rifle with this Faxon Firearms AR15 MIL-SPEC 5.56/300 Bolt to boost its reliability and cycling with every pull of the trigger. Specifications for Faxon Firearms AR Bolt Complete 5.56: Manufacturer: Faxon Firearms Color: Black Finish: Nitride Fabric/Material: 9310 Tool Steel Construction/S7 Tool Steel Construction Bolt Material: 9310 Steel Caliber: 5.56x45mm NATO Gun Model: AR-15 Condition: New Additional Features: Bolt Only Features: Bolt: 9310 Tool Steel Construction (Stronger than C158) Full MIL-SPEC Heat Treatment Shot Peened to MIL-SPEC Magnetic Particle Inspection (MPI) Back of Lugs Chamfered for Reliability Spring Insert & "Crane" O-Ring Installed QPQ - Salt Bath Nitrided Extractor: S7 Tool Steel Construction Fully Heat Treated Shot Peened Per MIL-SPEC QPQ - Salt Bath Nitrided Package Contents: Faxon Firearms AR-15 5.56/300 Bolt What firearm models does the manufacturer say Faxon Firearms AR Bolt Complete 5.56 is compatible with? The manufacturer says that Faxon Firearms AR Bolt Complete 5.56 is compatible with AR-15Faxon Firearms FF556BCNITRIDE: AR Bolt Complete 5.57 Black