Product DescriptionThe CMMG 5.7x28mm 5-inch Barrel and Bolt Carrier Group (BCG) Kit is built for creating an AR-platform pistol or short-barreled rifle (SBR) setup in 5.7x28mm. Using CMMGs patented Radial Delayed Blowback operating system, this kit helps reduce bolt carrier group weight and delivers less felt recoil compared to typical straight/direct blowback systems, while still supporting features such as last round bolt hold open (when used with compatible components). Designed to assemble into a mil-spec AR-15/Mk4 upper receiver, it can be used with a CMMG Mk57 lower receiver or a standard Mk4/AR-15 lower when paired with CMMG 5.7 AR conversion magazines.Product Highlights Complete barrel and BCG kit for AR-platform 5.7x28mm builds Patented CMMG Radial Delayed Blowback system for reduced felt recoil vs. straight blowback Designed to fit mil-spec AR-15/Mk4 upper receivers Compatible with CMMG Mk57 lowers or standard AR-15 lowers with proper conversion magazines Black finish to match a wide range of AR builds Specs Brand: CMMG Manufacturer Part Number: 57DBC33 UPC: 810097502390 Caliber: 5.7x28mm Barrel Length: 5 in Color/Finish: Black Includes: 5-inch barrel and 5.7x28mm bolt carrier group Operating System: Radial Delayed Blowback Platform Compatibility: Mil-spec AR-15/Mk4 upper; works with CMMG Mk57 lower or standard AR-15 lower (with CMMG 5.7 AR conversion magazines) Disclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the products manufacturer.