The.380 ACP is a rimless, straight-walled pistol cartridge developed by firearms designer John Moses Browning. The cartridge headspaces on the mouth of the case. It was introduced in 1908 by Colt, for use in its new Colt Model 1908 pocket hammerless semi-automatic, and has been a popular self-defense cartridge ever since, seeing wide use in numerous handguns. Other names for.380 ACP include.380 Auto, 9×17mm, 9mm Browning, 9mm Corto, 9mm Kurz, 9mm Short, and 9mm Browning Court. It should not be confused with.38 ACP. The.380 ACP does not strictly conform to cartridge naming conventions, named after the diameter of the bullet, as the actual bullet diameter of the.380 ACP is.355 inches.