If you’re looking to build the most compact 9mm AR then look no further. CMMG’s 9mm RDB uppers feature uncompromised design and engineering with styling that is never mistaken for something else. Having more options is always better like what magazines you would like to use. 9mm Uppers are designed to work with any standard AR15/Mk4 lower and 9mm AR Conversion Mags or our 9mm pistol magazine lower platforms: Mk9 (Colt-pattern mags) MkGs (Glock-pattern mags) Mk17 (Sig P320 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 9mm – Platform: Mk4 Mk9 Mk17 MkGs – Caliber: 9mm – Operating System: Radial Delayed Blowback – Barrel Length: 5 – Barrel Twist: 1:10 – 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 EML4 M-LOK – Finish: Cerakote Standard – Charging Handle: CMMG ZEROED Ambi – Weight: 2.6 lbs – Length: 13.7