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 RESOLUTE Upper Group with either our Mk57 Lower or a standard AR15 lower group and CMMG�s 5.7 AR Conversion Magazines and you�ll be ready to hit the range! Available in six different Cerakote finishes all CMMG Upper Groups come complete with bolt carrier group and ZEROED accessories including: - ZEROED AR15 Polymer Dust Cover - ZEROED AR15 Ambi Charging Handle - ZEROED Muzzle Brake 5.56mm - Platform: Mk4 Mk57 - Caliber: 5.7x28mm - Operating System: Radial Delayed Blowback - Barrel Length: 16.1 - Barrel Twist: 1:9 - Barrel Contour: MT - Barrel Material: 4140CM SBN - Muzzle Device: CMMG ZEROED Muzzle Brake - Muzzle Thread: 1/2 x 28 - Upper Receiver: Billet 6061 T6 Aluminum - Hand Guard: CMMG EML15 M-LOK - Finish: Cerakote Standard - Charging Handle: CMMG ZEROED Ambi - Weight: 4.0 lbs - Length: 25.3