The 9mm Steyr is a centerfire pistol cartridge originally developed for the Steyr M1912 military pistol. The cartridge headspaces on the mouth of the case. This was the service ammunition for Austria-Hungary during World War I and remained the service ammunition for Austria and Romania between the World Wars. It is similar to the 9×23mm Largo cartridge in performance, but their dimensions, while also similar, are just different enough to make them non-interchangeable. The cartridge performance is close to that of the .38 ACP. It is unrelated to the modern 9×23mm Winchester.