The 9x23mm Winchester is a pistol cartridge developed as a joint venture by Winchester Ammunition and Colt's Manufacturing Company. The 9x23mm Winchester has a convoluted development history, but was commercially introduced by Winchester in 1996. Marketed primarily to competition shooters as a replacement for .38 Super for International Practical Shooting Confederation, United States Practical Shooting Association and International Defensive Pistol Association competition, the cartridge made a splash, but never really caught on.
The critical design feature of the 9x23mm Winchester is a much strengthened case that does away with the semi-rimmed case design of the .38 Super which sometimes caused feeding problems. The strengthened case allows the 9x23mm Winchester to operate under a higher internal pressure, 40,000 CUP, in comparison to the maximum pressure of around 30,000 CUP for the .38 Super. It has a slightly tapered but nearly parallel case which means that it has greater magazine capacity for the same 9mm bore diameter relative to the necked down cases of the .357 SIG, 9×25mm Super Auto G, or 9×25mm Dillon. To achieve enough propellant capacity for the power needed the 9x23mm Winchester is longer than the 9×19mm Parabellum or .357 SIG and so requires the extra magazine front to back length of a 1911 style magazine.
