Mitchell Defense Enhanced AR-15 Carpenter 158 HP/MPI Bolt 5.56mm NATO/.223 Remington/.300 BLK Black. 56 NATO .223 Remington and .300 BLK platforms. Machined from Carpenter 158 steel and HP/MPI tested it offers superior strength and fatigue resistance. A billet extractor with O-ring ensures stable extraction while SP4-coated gas rings provide improved lubricity and increased longevity. This bolt is an excellent upgrade or replacement for AR-15 rifles that require consistent long-term reliability. Specifications for Mitchell Defense Enhanced AR-15 Carpenter 158 Bolt: Manufacturer: Mitchell Defense Color: Black Finish: Nitride Fabric/Material: Steel Caliber: 5.56x45mm NATO .300 AAC Blackout .223 Remington Gun Make: AR Platform Gun Model: AR-15 Features of Mitchell Defense Enhanced AR-15 Carpenter 158 Bolt Carpenter 158 bolt for superior tensile and fatigue strength Billet extractor with O-ring for improved extraction SP4-coated gas rings for extended service life Compatible with 5.56 NATO .223 Rem and .300 BLK platforms Ideal as a replacement or reliability-enhancing upgrade Package Contents: Mitchell Defense Enhanced AR-15 Carpenter 158 Bolt What firearm models does the manufacturer say Mitchell Defense Enhanced AR-15 Carpenter 158 Bolt is compatible with? The manufacturer suggests that Mitchell Defense Enhanced AR-15 Carpenter 158 Bolt is compatible with AR-15Mitchell Defense 651001: Enhanced AR-15 Carpenter 158 HP/MPI Bolt 5.56mm NATO/.223 Remington/.300 BLK Black