The Japanese launched the invasion of China in 1937, and what some consider the start of World War II, armed with Type 38 rifles chambered for 6.5x50mmSR. This was a good, rugged and accurate rifle firing an effective cartridge. Downside? It was overly long. Service load was a 139-grain .264-inch FMJ at approximately 2,500 fps. In comparison, this load would be a couple hundred feet per second slower than the modern 6.5mm Creedmoor, but shared many of its finer attributes. In use the 6.5x50mmSR had a flat trajectory, light recoil, possessed good accuracy and the projectile had a rapid yaw cycle increasing terminal performance.
The 6.5x50mm Semi-Rimmed (SR) was a product of the 19th Century arms race instigated by the French fielding of the smokeless powder 8x50mmR “Lebel” cartridge in 1886. The race towards a modern smokeless powder rifle cartridge led to many countries moving to much smaller bore-sizes compared to the traditional black powder cartridges. These included 7mm, 6.5mm and even 6mm for the US Navy. In 1897 the Imperial Japanese Army adopted the Type 30 Arisaka infantry rifle and carbine and with it a new small-caliber 6.5mm cartridge. The new 6.5x50mmSR replaced the older 8x53mmR Murata cartridge chambered in the Type 22 Murata rifle.
The new cartridge was initially loaded with a round-nosed cupronickel jacketed 160-grain projectile. Powder charge consisted of 31-grains of smokeless powder. It was loaded into a bottle-necked cartridge case with a case length of 50.3mm, rim diameter of 11.84mm (0.466-inch) and base diameter of 11.35mm (0.477-inch). Projectile diameter was 0.264-inch. Overall cartridge length came in at 74.68mm (2.94-inches). Unlike other contemporary designs the new Japanese design was neither fish nor fowl, not being rimmed or rimless but semi-rimmed.
The cartridge was updated with the adoption of the Type 38 rifle by replacing the 160-grain round nose projectile with a modern spitzer design. This weighed 139-grains, had a powder charge of 33-grains of smokeless which gave a muzzle velocity of approximately 2,500 fps. The new load offered noticeably improved exterior ballistics and better terminal performance. With the adoption of the Type 11 light machine gun in 1922 a reduced power load was introduced which reduced muzzle flash in the relatively short barrel.
The Japanese 6.5x50mmSR would live a long service life and served under many flags. It saw use with Imperial Japanese forces until the end of World War II. While it is best known for its Japanese service, it saw widespread use with Imperial Russian forces during World War I, the Revolution and the Civil War. Large numbers of Arisaka rifles were purchased by Russia and fielded due to their shortage of 7.62x54mmR M1891 rifles. The British also purchased large numbers of rifles beginning in 1914, which they mainly used for training. The 6.5x50mmSR was adopted by the British in 1917 as the .256-inch Mk II. They also equipped large numbers of Arabs with Arisakas to fight against the Ottoman Empire with. The Chinese also captured and reused huge numbers of Arisaka rifles during the Second Sino-Japanese War. Some Chinese units continued to field them during the Korean War. Not to be forgotten, Finland also fielded Type 30 and Type 38 rifles taken from Imperial Russian warehouses. These were used mainly by Finnish cavalry units before being relegated to the reserve, with many being sold to Estonia.
It should also be noted that the brilliant Russian designer Vladimir Fedorov spent considerable time studying the terminal performance of all the rifle cartridges fielded during the Russo-Japanese War of 1904/05. He made in-depth studies of the effects of the Japanese 8x53mmR Murata, 6.5x50mmSR and Russian 7.62x54mmR cartridges on flesh and bone and studied the wounds they made. While his work on wound ballistics is little known outside of Russia today, it led to him embracing the 6.5mm bore-size. While he designed a 6.5mm cartridge of his own, he eventually chambered his selective-fire Avtomat in the Japanese 6.5x50mmSR due to it already being in Imperial Russian service.
While the 6.5x50mmSR was an effective rifle cartridge, during World War II the Japanese Army came to the conclusion a larger, more powerful one was needed. This led to the development and adoption of the 7.7x58mm cartridge and Type 99 rifle. The 7.7mm Type 99 fired a 175-grain .311-inch FMJ at approximately 2,440 fps. While the 7.7x58mm made sense in a machine gun, providing a heavier payload, increased effective range and longer tracer burn it was a bit of a step backwards in a combat rifle. However, it provided commonality of ammunition with the Type 99 machine gun. Due to wartime demands though, the Japanese Army was never able to fully switch to 7.7x58mm, and 6.5x50mmSR rifles and machine guns remained front-line issue through-out the war.