The Windham Weaponry 9 mm Rifle (often seen as GMC or AR-9) is a pistol-caliber carbine built on an AR-pattern platform and chambered in 9x19 mm. Windham Weaponry produced it to suit the growing market for 9 mm carbines. Because it's in 9 mm and blowback-operated: Recoil is mild compared to rifle-caliber ARs. It's easy and inexpensive to shoot (shared ammo with your 9 mm pistol). It's handy for home defense, range fun, and training with cheaper ammo.