9x23mm Steyr

The 9x23mm Steyr was made in 1911 by Osterreichische Waffenfabriksgesellschaft for one pistol, the Steyr M1912, and it stayed with that pistol for its whole life. It is one of the small family of straight-walled 9 mm service rounds that appeared in the decade before the First World War, all sharing a 9.03 mm bullet and differing chiefly in how much case they put behind it.

The case is the round’s whole argument. At 23.2 mm it is 4.05 mm longer than a 9x19mm Parabellum, straight-sided, and only 0.08 mm narrower at the mouth than at the base, so it headspaces on the case mouth and the extractor has nothing but the groove to hold. Rim and base are both 9.7 mm. That extra length is what let the Austro-Hungarian round run a 115-grain bullet noticeably faster than a contemporary Parabellum out of a comparable barrel, and it is also why the two are not interchangeable in either direction despite the identical bullet.

The C.I.P. ceiling of 1350 bar is the number that dates the entry. It is low for a service pistol round — barely more than half what the same body allows for 9x19mm — and it is set that way because every gun still chambered for the cartridge is a century old. Modern commercial loadings sit well inside it, and the three that appear in the published record, from Hornady, Fiocchi and Hirtenberger, differ from each other by more than 60 m/s at the same bullet weight.

Gaps on this page: the three loads are the encyclopedia’s own ballistics table, which states a 128 mm test barrel for all of them and lists its ballistics sources as a numbered set that has to be read against the rows to know which maker produced which figure; that mapping is recorded in each note. No ballistic coefficient is published for any of them, and no wartime Austro-Hungarian service figure is available at all — everything here is either the modern C.I.P. standard or modern commercial ammunition.