The 5.7x28mm personal defense cartridge has found home with the purposefully designed 6.5" DISSENT upper group, all you need is a Mk4/mil-spec AR15 lower receiver or CMMG Mk57 lower receiver. All DISSENT uppers include a lower receiver 1913 picatinny rail end plate, Cerakote finish and CMMG's Zeroed Linear Compensator. With a compact action radial delayed blowback operating system and their proprietary bolt carrier group the DISSENT complete upper receiver from CMMG is ready for your next build!Features :Charcoal Green Cerakote Finish1/2X28 Muzzle ThreadingCMMG Zeroed Linear Compensator7075 T6 Aluminum ConstructionM-LOK Proprietary Free Float Handguard"6.5", 1:9 Twist Barrel"