.380 ACP

Test barrel length: 3.75 inches (95.3 mm)
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The .380 ACP (Automatic Colt Pistol), also known as .380 Auto, .380 Automatic, or 9×17mm, is a rimless, straight-walled pistolcartridge that was 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 1903 Pocket Hammerlesssemi-automatic, and has been a popular self-defense cartridge ever since, seeing wide use in numerous handguns (typically smaller weapons). Other common names for .380 ACP refer to it with the metric system and use the shorter length or different inventor to discern from 9mm Luger, such as 9mm Short, Corto, or Kurz (English, Italian, and German, depending on context), or 9mm Browning and 9mm Browning Court, the C.I.P. designation using both ("Court" being the French word for 'Short' as the C.I.P. is based in France). It should not be confused with .38 ACP that John Moses Browning had also invented prior. 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.