Grabbing some mags for your Radial Delayed Blowback 9mm? These Gen II 9mm magazines work in Mk4/AR15 lower receivers with a CMMG 9mm Radial Delayed Blowback upper and feature 10rd capacity and iconic CMMG styling. Exterior dimensions closely match those of common 5.56 AR15 magazines for cross-compatibility with existing mag pouches and carriers.