Most who know the 5.7x28 mm cartridge don’t know that CMMG Inc., a U.S. manufacturer, is chambering an AR-pistol to operate the Belgian-designed “Five-Seven” cartridge. The Mk57 Banshee pistol, featured here, operates different than the typical Stoner, gas-operated design. This Slate Gray-Cerakoted, 4 1/2-lb. pistol, built from both forged and billet aluminum, utilizes a delayed form of cartridge blowback termed "radial-delayed" by the manufacturer. To find out more, watch this week's NRA Gun of the Week video hosted by Kelly Young.