6.5x50
Irwin,
Japan was the first country to adopt 6.5 calibur, way back in 1897 when most other countries were tinkering with the calibur. It served Japan through the two World wars. Japanese indeed produced very good quality steel, and even exported steel to Britain and France during the first World War (Japan joined the allies during the WWI.) In the 1930's after Japan engaged in a war with China, Japan couldn't keep up with the steel demand and depended on US steel import. Note that while Germany, Britain, Japan all produced good quality steels, US produced better steels in far more quantities than anyone. Especially in Britain's case, we provided for 70% of their steel consumption during the WWII, not counting the steel we provided them in finished form (tanks, etc.) all for essentially free.
Anyway, the Arisaka Model 38 bolt action rifle was adopted for the 6.5x50 cartridge in 1905. The Arisaka is an ungainly looking but very safe modified Mauser bolt action rifle of great strength. I have read that during testing to destruction after the end of WW II the Arisaka Model 99 (a modified design in 7.7x58mm) survived pressures that destroyed all of the other famous bolt action rifles of WW II, including the American 1903 Springfield and German Mauser Model 98 rifles. Not many Westerners realize that the Japanese Arisaka service rifle of WW II was the strongest military bolt action rifle ever produced.
the 6.5x50 cartridge was replaced with 7.7x58 based on Japan's experience during the war with China which started in earnest in 1936. 6.5x50 round, while very accurate and had low recoil, was not as good a man stopper as 8mm mauser or 30-06. During the battle of Sanjing, China, where Chinese troops charged Japanese position in overwhelming numbers, a chinese soldier was shot five times and still reached the Japanese line at which point a Japanese officer cut him down with a sword. The bigger problem still was the lack of penetrating power of 6.5 cartridge. Chinese troops using 8mm mauser and American supplied 30-06 rounds could easily shoot through the Earthen walls of Chinese buildings and kill the Japanese whereas 6.5 couldn't penetrate the walls reliably. During the city battles, Chinese often shot through walls at the concentrated Japanese moving columns from inside the homes (I'm not sure how the Chinese aimed though). But all in all, I think 6.5x50 was an excellent round, and in many aspects, it was ahead of its time. 6.5x50 would've made an excellent assault rifle round.