Personal defense calibers like 5.7x28mm have gained popularity in recent years, offering PDW (Personal Defense Weapon) ballistics with the classic style and balance of a carbine. If you're considering this setup, the RESOLUTE Upper Group from CMMG is an excellent choice. Pair it with either our MK57 Lower or a standard AR-15 lower group along with CMMG's 5.7 AR conversion magazines and you'll be prepared for the range or personal defense scenarios. Originally developed for the .45 ACP MKG platform, CMMG has applied their Radial Delayed Blowback system across their pistol caliber lineup. This innovative system reduces recoil impulse and optimizes bolt weight, providing a softer shooting experience compared to traditional straight blowback systems. For a detailed exploration of Radial Delayed Blowback, delve into CMMG's comprehensive articles and video resources. It's important to note that CMMG recommends using their .40 S&W MKGs uppers exclusively with MKGs lowers to ensure reliable functionality and performance.