7.7×58mm Arisaka

The 7.7×58mm Arisaka, formally the Type 99 7.7mm rimless, is a rimless bottlenecked rifle cartridge adopted by the Imperial Japanese Army in 1939 for the Type 99 rifle and the Type 99 light machine gun. It replaced the earlier semi-rimmed 7.7×58mm Type 92, itself a rimmed adaptation of the 6.5×50mm Arisaka’s replacement programme, in Japan’s move toward a rimless cartridge more suited to belt-fed machine-gun use — a change driven directly by feeding problems the semi-rimmed Type 92 round caused in automatic weapons.

Dimensionally it echoes the German 8×57mm IS that its designers studied closely, at a similar case length and shoulder geometry but a narrower 7.92 mm bullet diameter matched to Japan’s existing 7.7 mm bore standard. Japan fielded three related but distinct 7.7 mm cartridges during the Second World War — the semi-rimmed Type 92, the rimless Type 99, and a rimmed naval aircraft variant — a proliferation that caused real wartime confusion between round and chamber.

This entry carries dimensions from the cited Wikipedia infobox, recorded as estimated because no free dimensional standard exists for this cartridge from any standards body. One ball load’s bullet mass is recorded, also estimated and converted from a published 182 grains; no source states a test barrel length for any published velocity figure, so none is recorded and the cartridge computes no muzzle energy or trajectory. No maximum pressure figure is published free for it either.