Having a .45 ACP pistol-caliber carbine requires the use of a bolt that's designed to provide reliable operation with the round, and the Stern Defense AR-15 SD-BU45 Bolt Carrier is purpose-built to provide the reliable, dependable, durable operation needed in a big-bore PCC. Each Stern Defense AR-15 SD-BU45 Bolt Carrier is machined from 8620 AISI steel and features a 4140 billet-steel extractor that ensures ejection every time. The carrier features a Glock®cut and is treated with a manganese-phosphate finish. The bolt works in all mil-spec and Glock-pattern AR-15 upper receivers and is compatible with standard AR-15 charging handles. The carrier includes the firing pin, spring, retaining pin, extractor and extractor spring. One of the stand-out features of this Stern Defense AR-15 SD-BU45 Bolt Carrier is the new bolt design that's compatible with single-stage triggers that have short resets. The bolt is compatible with the Law Tactical folding-stock adapter, as well as the Echo trigger. The bolt must be used with an 11-ounce or heavier buffer, and upper receivers must have an enlarged ejection port to accommodate the large-diameter brass. The bolt is compatible with JP Silent Capture springs, but Stern Defense does not recommend this use, as .45 ACP can damage the JP system.