Gaining more acceptance as the go to personal defense caliber for many shooters in recent years has proven itself to be well suited for the job. With incredibly flat shooting performance and low recoil, caliber excels at closer ranges while still providing ideal penetration. Equipped with a 5 barrel. CMMG uppers are designed to work with CMMG Mk57 lowers or standard AR15/Mk4 lowers (when used with 5.7 AR Conversion Mags).