In 2018, CMMG announced its Banshee Mk57 lineup, which uses the 5.7x28mm cartridge popularized by the FN (Five-seven) and PS90 but found in almost no other firearms. The action is constructed with a delayed, radial blowback design for 5.7x28mm chambering. In RBD, the blowback operation often found in pistol-caliber AR-type guns is combined with some aspects of a regular direct-impingement AR-­15. Each lower receiver is made to suit the Five-seven pistol mag and is machined from a single piece of aluminum billet. This meant that the Mk57 Banshee could not be modified to use a conventional AR-­15 lower receiver with an insert in the magazine well. Two buffer weights are included with CMMG's Mk57 Banshee: a standard and a lightweight (standard for 40-grain ammo and most suppressed use, and lightweight for 27 and 28-grain ammo and subsonic fodder). The Mk57 is a great option for shooting due to its lack of recoil, small weight, sufficient magazine capacity, and centerfire cartridge reliability.