6.5x50mmSR Arisaka

The 6.5x50mmSR was the Imperial Japanese Army’s service cartridge from 1897, adopted as the Type 30 round together with the Type 30 rifle it is named after, and it replaced the 8x52mm Murata. Japan went to a small bore earlier and more completely than any other great power, and spent the next forty years arguing about whether that had been a mistake.

Its head is the interesting part. The rim is 12.08 mm against a base of 11.45 mm, so it stands 0.63 mm proud — enough to headspace and extract on, not enough to make the round awkward to stack. That semi-rimmed compromise is why the case feeds from the Type 38 rifle’s box magazine and from the Type 11 light machine gun’s hopper, and it is a very different answer from the fully rimmed 7.62x54mmR or .303 British of the same generation. The case is 51 mm by the C.I.P. drawing, which is why the European standards body files the round as 6,5 x 51 R while everyone else rounds it down.

The load changed once, decisively. The 1897 Type 30 round carried a round-nosed cupronickel bullet of about 10.4 g; in 1907 Japan followed the rest of the world to a pointed bullet, and the Type 38 cartridge recorded here fires a 9.0 g spitzer at about 770 m/s from an 800 mm barrel. A third variation was made for the Type 11 light machine gun in the 1920s, whose 17.5-inch barrel produced a flash the rifle load did not; the answer was a reformulated propellant rather than a new case, and the resulting round was marked with a coloured ring.

Its reputation was made twice over by other people’s rifles. Russian designers who had been shot at with it in 1904-05 chambered the Fedorov Avtomat for it, on the grounds that 7.62x54mmR recoiled too hard for an automatic; Britain bought about 150,000 Arisakas in 1914 and had Kynoch make the ammunition. Japan itself began replacing it with the 7.7x58mm from 1938 and never finished, which left its forces supplying two rifle cartridges through the whole of the Pacific war.

Gaps on this page: only the Type 38 ball load is recorded, because it is the only one for which a velocity and a barrel length are published together — the Type 30 round-nosed load, the reduced-flash machine-gun round and the 1932 armour-piercing round have masses or descriptions but no matched pair. No ballistic coefficient is published for any of them. The C.I.P. dimensions transcribed here are the modern commercial standard rather than an Imperial Japanese Army drawing, and its 6.63 mm bullet maximum contradicts the 6.705 mm given in the encyclopedia’s own opening sentence; the datasheet figure, which the same article’s infobox repeats, is the one recorded.