The concept of a 9mm AR is nothing new. In the early 1980s, Colt began developing 9mm prototypes based on this platform, the earliest of which was an open-bolt submachine gun that fed from a modified Uzi magazine. In subsequent prototypes, the design switched to a closed-bolt direct blowback system — this would carry through to Colt’s first production version, the 10.5-inch-barreled R0635 SMG. Since then, direct blowback has become the industry standard for 9mm ARs, with a few notable exceptions (for example, the radialdelayed CMMG Banshee featured in Issue 16 and the roller-delayed JP-5 we reviewed in RECOIL Issue 57).
If we’re being generous, we’ll just call direct blowback simple. Otherwise, we might call it downright crude. Either way, rather than relying on a mechanical delay mechanism to slow down the bolt, it relies on the mass of the bolt and buffer system. This
