7.7x56R vs. 7.7x58R?


I see the .303 British cartridge listed as both the 7.7x56R and the 7.7x58R and the 7.7 Japanese listed as 7.7x58R and interchangeable with the .303 British.

Which is correct?

The case length of the .303 is listed as 2.222" (or thereabouts) which is 56.4mm, so you can’t round that up to 58mm…



AKMS: the .303 British has a nominal metric case length of 56 m/m, including those produced in Italy, Japan, and elsewhere. The Japanese 7.7 m/m rimless and semi-rimmed cartridges do have a case length of 58 m/m. Jack


I know of no common military 7.7x58R (Rimmed), the Japanese used 7.7x58 Rimless and 7.7x58SR (Semi-Rimmed). To further complicate the issue, the Japanese also used .303 ammo, AKA 7.7x56R.


Thank you for the clarification gentlemen. As is usual, there is misinformation on the 'net and the Japanese “7.7x58R” is one of them…



To provide a little more information, by WW2 the 7.7x56R (.303) was used only by the Japanese Navy in aircraft guns (they still had modified versions of the old Lewis and Vickers guns in service).

The 7.7x58SR and 7.7x58 were Japanese Army cartridges, not used by the Navy. The 7.7x58SR was only used in MGs, the 7.7x58 was introduced about a decade later (around the start of WW2) and was used in both MGs and rifles.

Also, both the Navy and Army used the 7.92x57 calibre in German aircraft MGs.