CMMG Mk4 9mm Resolute Upper Group Receiver 16.1in Titanium. We have you covered Utilizing our Radial Delayed Blowback operating system not only does this upper create one of the softest shooting 9mm PCCs with style that is unmistakably CMMG this upper group is designed to work with a number of different lower receivers. From standard AR15 lowers (when used with AR 9 conversion mags) to any of our pistol magazine lowers (Mk9 MkGs and Mk17) you can build your next PCC exactly how you imagine. Specifications for CMMG Mk4 9mm Resolute Upper Group Receiver: Manufacturer: CMMG Caliber: 9mm Luger Overall Length: 25.3 in Barrel Length: 16.1 in Barrel Profile: Medium Tapered Barrel Twist Rate: 1-10 Muzzle Device: CMMG Zeroed Muzzle Brake Fabric/Material: 6061-T6 Aluminum Gun Rail: M-LOK Gun Make: CMMG Gun Model: CMMG Mk4 Weight: 4 lb Magazine Included: No Condition: New Mount Type: M-LOK Threads per Inch: 1/2x28 Package Contents: CMMG Mk4 9mm Resolute Upper Group Receiver What firearm models does the manufacturer say CMMG Mk4 9mm Resolute Upper Group Receiver is compatible with? The manufacturer suggests that CMMG Mk4 9mm Resolute Upper Group Receiver is compatible with CMMG Mk4CMMG 99BE6B6-TI: Mk4 9mm Resolute Upper Group Receiver 16.1in Titanium