.25 ACP
The .25 ACP (Automatic Colt Pistol), also known as the .25 Auto, .25 Automatic, 6.35mm Browning, or 6.35×16mmSR is a semi-rimmed, straight-walled centerfire pistol cartridge introduced by John Moses Browning in 1905 alongside the Fabrique Nationale M1905 pistol. == Design and history == The .25 ACP (6.35mm Browning) was designed as a .25-inch diameter caliber due to .25 inches being the smallest diameter caliber that John Browning could possibly configure while still retaining a centerfire primer pocket.