7.7 X 58 Jap
The 7.7×58mm Arisaka cartridge or Type 99 rimless 7.7 mm was chambered in the World War II Arisaka Type 99 Rifle. The cartridge was designed to replace the aging 6.5×50mm Arisaka cartridge after seeing the effectiveness of the 8×57 IS heavy machine gun in action in China during 1937. Due to lack of materials the plan to phase out the 6.5 mm Arisaka cartridge by the end of the war was not completed.
While the round chambered by the Arisaka rifle used a rimless case, rimmed and semi-rimmed variants were produced for use in some Japanese machine guns. This machine gun ammunition is more powerful, and the altered rim is meant to prevent it from being chambered in a rifle. The 7.7 mm Arisaka uses the same .311–.312″ bullets as the .303 British, and its cartridge case is similar in power to the .30-06 Springfield (7.62×63mm). Factory loaded ammunition and brass cases are available from Norma and Graf; Hornady, Sierra and Speer also produce usable bullets. Reloadable cartridge cases can be produced by reforming .30-06 brass, or fire forming 7.92×57mm cases. Case heads derived from the .30-06 will be slightly undersized and will bulge slightly just ahead of the web on firing, while the 7.92×57mm derived cases will be slightly short. Normal cases of the correct dimensions will also bulge slightly, however, as most Japanese rifles of this era had slightly oversized chambers, intended to allow the bolt to be closed on a round even in a very dirty chamber. Reloading data for .303 British is a good starting point for load development, since the two cartridges are nearly identical in power and size.
The 7.7×58mm Arisaka as a sporting cartridge is suitable for most big game with proper bullet selection.