AR-9 refers to an AR-15-pattern firearm chambered in 9mm Luger, built as a pistol-caliber carbine or pistol using a blowback action instead of direct impingement gas operation. AR-9 uppers and lowers use dedicated 9mm bolts and magazine wells, often accepting common Glock- or Colt-pattern pistol magazines, for low-cost, low-recoil shooting on a familiar AR-15 platform.