Designed to provide superior ballistics and less felt recoil than most pistol caliber personal defense weapons 5.7x28mm has quickly become one of the most popular chamberings in the PDW space. With the 8 BANSHEE upper group you can build the PDW AR15 of your dreams. Compatible with either CMMG Mk57 lowers or a standard AR15/Mk4 lower (when used with CMMG 5.7 AR Conversion Mags). 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 Linear Compensator 5.56mm - Platform: Mk4 Mk57 - Caliber: 5.7x28mm - Operating System: Radial Delayed Blowback - Barrel Length: 8 - Barrel Twist: 1:9 - Barrel Contour: MT - Barrel Material:4140CM SBN - Muzzle Device: CMMG ZEROED Linear Compensator - Muzzle Thread: 1/2 x 28 - Upper Receiver: Billet 6061 T6 Aluminum - Hand Guard: CMMG EML7 M-LOK - Finish: Cerakote Standard - Charging Handle: CMMG ZEROED Ambi - Weight: 2.9 lbs - Length: 16.5