|6.5×50mm SR Arisaka|
|Place of origin||Japan|
|Used by||Japan, Russia, United Kingdom, China, North Korea, South Korea, Thailand, Finland, Indonesia, Cambodia, Poland|
|Wars||Russo-Japanese War, World War I, Second Sino-Japanese War, World War II, Indonesian War of Independence, Korean War|
|Case type||Semi-rimmed, bottlenecked|
|Bullet diameter||6.705 mm (0.2640 in)|
|Neck diameter||7.34 mm (0.289 in)|
|Shoulder diameter||10.59 mm (0.417 in)|
|Base diameter||11.35 mm (0.447 in)|
|Rim diameter||11.84 mm (0.466 in)|
|Rim thickness||1.143 mm (0.0450 in)|
|Case length||50.39 mm (1.984 in)|
|Overall length||75.69 mm (2.980 in)|
|Primer type||Large rifle|
|139 gr (9 g) FMJ||770 m/s (2,500 ft/s)||2,615 J (1,929 ft·lbf)|
|Test barrel length: 800 mm|
The 6.5×50mm Semi-Rimmed (6.5×50SR) Japanese cartridge, currently manufactured under the designation 6.5mm Jap, was adopted by the Imperial Japanese Army in 1897, along with the Type 30 Arisaka infantry rifle and carbine. The new rifle and cartridge replaced the 8×52mm Murata round used in the Type 22 Murata Rifle. In 1902 the Imperial Japanese Navy chambered its Type 35 rifle for the cartridge as well. In 1905, the round also came to be offered in the Type 38 Arisaka infantry rifle and carbine, both of which rendered the Type 30 obsolete in Imperial Army service. Type 44 cavalry carbines, first adopted in 1911, were also chambered in 6.5×50mm.
Early 6.5×50mm cartridges had a cupronickel round nosed bullet weighing 10.4 grams (160 gr) fired with approximately 2.0 grams (31 gr) of smokeless powder. This was later changed with the adoption of the Type 38 when Japan, in line with the other great powers around the same time, changed to the pointed or spitzer bullet in the first decade of the twentieth century. The Type 38 spitzer-bullet round fired a 9.0-gram (139 gr) bullet with a powder charge of 2.5 grams (39 gr) for a muzzle velocity of around 770 metre per second (2,500 ft/s).
The round was criticized for being underpowered compared to other, more powerful American and European cartridges such as the .30-06, .303 British, 7.92×57mm Mauser, and 7.62×54mm Russian. For this reason it was later replaced by the more powerful 7.7×58mm cartridge.
The Type 38 spitzer version of the 6.5×50mm cartridge remained unchanged until after the adoption of the Type 11 light machine gun in 1922. The Type 11 was initially meant to fire standard Type 38 rifle ball ammunition by means of ordinary five-shot Type 38 stripper clips. Subsequent use indicated that the higher pressures generated by the standard rifle ammunition caused parts wear and breakage in machine guns. It was thus decided to reduce the powder charge of the Type 11's 6.5 mm ammunition to overcome the problem. This reduced charge 6.5 mm ammunition can be identified by a letter "G" in a circle stamped on the outside of the ammunition packaging which stands for the first letter of genso - the Japanese word for "reduced." This special ammunition was also issued to soldiers carrying the Type 96 light machine gun introduced in 1936 and to snipers issued the Type 97 sniper rifle, introduced in 1937. The advantage of the reduced charge ammunition to the sniper was it aided in his concealment as the reduced charge rounds produced less muzzle flash than standard rounds and thus did not give away the sniper's position.
Also produced was 6.5mm gallery ammunition, incorporating a paper or wood bullet; and dummy rounds, which were issued to Japanese forces. These were either all brass rounds or were more commonly red varnished wood with a metal base and rim. Ammunition used in the spigot-type Japanese grenade launchers often has paper bullets and can be identified by the staked primers.
 Other 6.5 mm firearms
Other 6.5×50mm long-arms used by Japan included a few Type 13 Mauser rifles produced at Hoten (Mukden) Arsenal in Manchuria, China. These rifles were built on Danish Nielsen & Winther machinery originally for the Manchurian warlord Chang Tso Lin beginning in 1924. When Japan took over the arsenal after the Manchurian Incident of 1931 the Type 13 rifle continued to be produced in 7.92×57mm Mauser caliber, however an unknown number were also produced in 6.5×50mm. The Type I rifles built by Italy for Japan under the terms of the Anti-Comintern pact from 1939 to 1943 are in standard 6.5×50 mm Japanese. Their Italian origin should not be taken to mean that these will safely fire the longer, but outwardly similar, 6.5×52mm Carcano round. An unknown number of Dutch M1895 Mannlicher rifles and carbines captured by Japanese forces during the seizure of the Dutch East Indies in 1942 were converted to 6.5×50mm from the 6.5×53mm Dutch rimmed chambering.
 Russian usage
After observing the effectiveness of the Type 30 6.5×50mm round used against them during the Russo-Japanese War of 1904–1905, leading Russian arms designers chambered early Russian semi-automatic rifle designs for the Japanese round. Since the standard Russian military rifle cartridge of the time, the 7.62×54mmR rimmed round, was too powerful and generated excessive recoil in an automatic weapon a 6.5 mm round was seen as more appropriate. Early designs by Vladimir Fedorov utilized 6.5×50 mm, including the Fedorov Avtomat rifle which was actually issued to troops, though in small numbers. Later, Russian troops on the Armenian front were issued with Type 38 carbines by the Tsar's government. Russians also tended to modify the Type 38's magazine latch, as it was found that gloved hands would sometimes inadvertently nudge the magazine release and dump the ammunition.
 British usage
In 1914 approximately 150,000 Arisaka Type 30 and Type 38 rifles and carbines were sold to British forces (mainly to the Royal Navy), where they were used for training. The 6.5×50mm round was subsequently produced in Britain by the Kynoch company and was officially adopted for British service as the .256-inch (6.5 mm) caliber Mk II in 1917. The Arab armies organized by British Captain T. E. Lawrence to fight against the Ottoman Empire during World War I are purported to have been issued with Type 30 rifles by the British in 6.5 mm though some have opined that the Bedouin forces mainly used captured Ottoman Mausers instead. In all, the 6.5×50 mm Japanese semi-rimmed round has been used in either Japanese or domestically designed weapons by Japan, Russia, the United Kingdom, China, North Korea, South Korea, Thailand, Finland and Indonesia. Many of the British Naval Arisakas were given to the White Russians.
 Finnish usage
The Russians, having a surplus of Type 30 and Type 38 rifles from both direct purchase from Japan during WWI and also having captured examples during the Russo-Japanese War, warehoused some of these rifles in Finland. During the Russian Revolution, many Finns seized the chance for independence and took Arisakas from Russian arsenals. They were used mainly by Finn cavalry and after Finland's independence, experiments were taken to upgrade the Type 38s to 7.92 Mauser. With parts and ammunition drying up, Finland relegated the Arisaka to the reserves and the merchant marines before trading a large number of them off to Estonia. Finnish-issued Arisakas will have district numbers and an 'S' branded on the stock.
As Arisaka rifles have increased in popularity with collectors, modern manufacture has resumed. The cartridge is available for retail in Europe and North America, and is manufactured by Norma of Sweden, Precision Cartridge Inc., and Hornady. Brass cases are also manufactured and sold by Prvi Partizan for purposes of hand loading. Reloadable Boxer-primed cases are sometimes produced by reforming .220 Swift brass. Bullets are .264 caliber.
 See also
- The 6.5×50 Arisaka (6.5 mm Japanese) - by Chuck Hawks
- THE .256" BRITISH: A LOST OPPORTUNITY - British use of the 6.5×50mm
- The 6,5×50 Arisaka By Giovanni Defrancisci