With strength in mind, Toolcraft made their Bolts from heavy duty 9310 Alloy Steel and their Bolt Carriers from 8620 case-hardening aircraft grade steel. 9310 steel has a high core strength rating, high fatigue strength, and a high hardenability rating overall. Normally, 9310 steel is used for gears and crankshafts in massive trucks and large aircraft, so its easy to see why it would make an ideal Bolt for an AR. Why 9310 instead of Mil-Spec Carpenter 158 steel? Simple, 9310 is an AISI standard grade tool steel which, when properly treated, actually makes it about 7% stronger than "mil-spec" Carpenter 158. The proof is in the numbers. The carrier material, 8620 is used for various aircraft and vehicular applications, has a superior toughness rating, and features solid overall strength properties. So when you combine these two outstanding steels with Toolcraft's superb machining, you get a BCG that is an optimal choice for your next 458 SOCOM or 450 Bushmaster AR build.The Toolcraft 458 SOCOM/450 Bushmaster Bolt Carrier Group comes in the Salt Black Nitride finish to upgrade your existing AR build with an excellent, long lasting BCG. These Full Auto M16 Profile Direct Impingement BCG designs have multiple features that separate them from the average AR Bolt Carrier Group on the market. These BCGs are Magnetic Particle Inspected for Quality Control, and built to strict Mil-Spec standards throughout. They have Mil-Spec 8740 Steel hard-chromed Firing Pins, Mil-Spec Gas Keys with Grade-8 screws that are staked and sealed with Permatex No.3, and they have shot-peened case-hardened D2 tool steel extractors. These Toolcraft Inc. BCGs come from the factory with a Lifetime Replacement Warranty on the entire Bolt Carrier Group. Plus, with the AR15Discounts satisfaction guarantee, you can buy your AR build components without apprehension. Our guarantee says if you are unhappy for any reason, you can send it back to us within 30 days for a full refund. No worries. At the time this was written, these excellent BCGs had dozens of 5-STAR ratings from around the web making them an exquisite choice for your next 458 SOCOM/450 Bushmaster AR build. Get yours today!NOTE- The Salt Black Nitride BCG offers the dark, subdued finish that doesn't change the specs of the Bolt Carrier, but it still makes the outside of the Bolt Carrier harder. This treatment increases the longevity of the part, makes it extremely wear resistant and durable, and this treatment protects the part from corrosion.Technical Specs:* Gas system: Direct Impingement* Caliber: 458 SOCOM/450 Bushmaster* Finish: Salt Black Nitride* Bolt: 9310 Alloy Steel (High Hardness)* Carrier: 8620 Aircraft Grade Steel* Extractor: Shot Peened and Case Hardened D2 Tool Steel* Firing Pin: Mil-spec 8740 steel with hard chrome finish* Gas Key: Mil-Spec w/ properly staked Grade-8 screws & Permatex No. 3 sealed* Cam Pin: 8620 Steel w/ Black Nitride Finish* Quality Control: MPI Inspected for QC