Product DescriptionThe CMMG 16.1-inch 5.7x28mm Barrel and Bolt Carrier Group (BCG) Kit is designed for builders who want to assemble a carbine-length AR-platform upper using CMMG's patented Radial Delayed Blowback operating system. Compared to typical straight blowback systems, Radial Delayed Blowback reduces felt recoil while maintaining key functionality such as last-round bolt hold open. This kit is intended to be assembled into a Mk4/mil-spec AR-15 upper receiver and can be used with a CMMG Mk57 lower receiver or a Mk4/AR-15 mil-spec lower receiver when paired with CMMG 5.7 AR conversion magazines.Product HighlightsComplete AR-platform barrel and bolt carrier group kit for building a 5.7x28mm carbine-length upperPatented CMMG Radial Delayed Blowback system for reduced felt recoil versus standard blowbackDesigned to retain last-round bolt hold open functionality16.1-inch threaded barrel for compatibility with muzzle devices and suppressor-ready buildsMade to assemble into Mk4/mil-spec AR-15 uppers and work with Mk57 or AR-15 mil-spec lowers (with conversion magazines)SpecsBrand: CMMGManufacturer Part Number: 57D0476UPC: 810097502413Cartridge: 5.7x28mmBarrel Length: 16.1 inMuzzle: ThreadedColor/Finish: BlackOperating System: Radial Delayed BlowbackCompatibility: Mk4/mil-spec AR-15 upper; works with CMMG Mk57 lower or Mk4/AR-15 mil-spec lower (with CMMG 5.7 AR Conversion Magazines)Included Components: Barrel; Bolt Carrier GroupDisclaimer: 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 product's manufacturer.