The CMMG unique Radial Delayed Blowback (RDB) operating innovation has been used to bring the company's oldest 9 mm pistol-caliber platform, the Mk9, in line with other Banshee and Resolute models. Colt SMG-style stick magazines are compatible with Mk9 versions. The Banshee Mk9 is basically a blow-back operated pistol, just like other RDB variants. The bolt carrier group (BCG) is driven back by the pressure created by the cartridge, as opposed to other AR platforms' use of a gas-impingement or piston mechanism. The upper receiver of the Mk9 has a flat top and a Picatinny rail, and it is made of forged 7075-T6 aluminum. A Picatinny top rail and a useful handstop are both included in the CMMG RML4 4" M-LOK handguard that is attached to it. Dust cover, forward-assist button, and CMMG's large ambidextrous charging handle are also placed on the upper receiver. A special Colt SMG magazine well is found in the lower receiver and can hold 10-, 20-, and 32-round magazines that lock the bolt open after the last round is fired. The AR-15's typical design is present in the bolt catch, magazine release, trigger group, and ambidextrous safety. The polymer trigger guard and detachable pistol grip are both of the typical AR-type and are both Magpul MOE parts. This pistol-caliber AR handgun is certainly worthy of consideration.