Personal defense calibers like 5.7x28mm have become a big thing in the last few years, and if you're looking for PDW ballistics and the classic style and balance of a carbine then you're in luck. Combine this RESOLUTEUpper Group with either our Mk57 Lower or a standard AR15 lower group and you'll be ready to hit the range! Available in multiple Cerakote finishes, all CMMGUpper Groups come complete with bolt carrier group and ZEROED(TM) accessories including:ZEROED AR15 Polymer Dust CoverZEROED AR15 Ambi Charging HandleZEROED Muzzle Brake 5.56mmWith the wide range in ammunition available, and the option for suppressed operation, the available Action Tuning Kit will allow you to tune your system even more for added flexibility and smoother operation.Radial Delayed Blowback(TM) Operating SystemOriginally developed for the .45 ACP MkG platform, CMMG has adapted our Radial Delayed Blowback system across our pistol caliber lineup to create pistols and rifles with a softer recoil impulse and reduced bolt weight compared to traditional straight blowback systems. Check out our CMMG Resources article & video to learn more about what sets Radial Delayed Blowback apart.Lifetime Quality GuaranteeWe aim to please, that's why every CMMG product is backed by our Lifetime Quality Guarantee against material and workmanship defects. Learn More.