CMMG Magazine, 5.7X28MM, 10 Rounds, Fits CMMG MK4/AR15, Matte Finish, Black 54AFC44 Redesigned with a brand-new look" CMMG's 5.7 AR Conversion Magazines feature a number of improvements. From the new stylized texture grip and 5.7x28mm engraving on the sides to the upgraded feed lips" these magazines are built to exceed your expectations. 5.7 AR Conversion Mags are available in 10 or 32 round capacity and are designed to work with CMMG 5.7x28 Radial Delayed Blowback Uppers and Mk4/Mil-Spec AR15 lower receivers.