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|Type 99 7.7 mm rimless|
|Place of origin||Japan|
|Variants||Type 92 semi-rimmed 7.7 mm|
|Bullet diameter||7.89 mm (0.311 in)|
|Neck diameter||8.07 mm (0.318 in)|
|Shoulder diameter||10.89 mm (0.429 in)|
|Base diameter||11.99 mm (0.472 in)|
|Rim diameter||12 mm (0.47 in)|
|Rim thickness||1.0 mm (0.039 in)|
|Case length||57.66 mm (2.270 in)|
|Overall length||79.5 mm (3.13 in)|
|Primer type||Large rifle|
|Type 92 semi-rimmed 7.7 mm|
Various Type 92 rounds
|Type||Machine gun round|
|Place of origin||Japan|
|Wars||Second World War|
|Variants||Type 99 rimless 7.7 mm (Arisaka), Navy type 7.7 mm|
|Case length||2.25 in (57 mm)|
|Overall length||3.14 in (80 mm)|
The 7.7×58mm Arisaka cartridge, Type 99 rimless 7.7 mm or 7.7mm Japanese was a rifle cartridge which was used in the Imperial Japanese Army's Arisaka Type 99 rifle and machine guns, and was the standard light cartridge for the Imperial Japanese Army Air Service, such as the Type 89. The Imperial Japanese Navy (and Imperial Japanese Navy Air Service) never shared weapons or ammunition with the army, instead adopting the 7.7x56mmR, a direct copy of the .303 British round. The cartridge was designed to replace the aging 6.5×50mm Arisaka after seeing the effectiveness of the MG 34 GPMG in action (firing 8×57mm IS full power military rifle ammunition) in China during 1937. Due to a lack of materials, the plan to phase out the 6.5 mm Arisaka cartridge by the end of the war was not completed.
While the round chambered by the Arisaka rifle used a rimless case, rimmed and semi-rimmed variants were produced for use in some Japanese machine guns. This machine gun ammunition is more powerful, and the altered rim is meant to prevent it from being chambered in a rifle. The 7.7 mm Arisaka uses the same .311–.312" bullets as the .303 British, and the standard military load delivered the same muzzle energy as the .303 British. Factory loaded ammunition and brass cases are available from Norma and Graf; Hornady, Sierra and Speer also produce usable bullets. Reloadable cartridge cases are produced by reforming .30-06 brass, or fire forming 8x57mm IS cases. Case heads derived from the .30-06 are slightly undersized and bulge slightly just ahead of the web on firing, while the 8×57mm IS derived cases are slightly short. Normal cases of the correct dimensions also bulge slightly, however, as most Japanese rifles of this era had slightly oversized chambers, intended to allow the bolt to be closed on a round even in a very dirty chamber. Reloading data for .303 British is often used for load development, since the two cartridges are nearly identical in power and size.
The 7.7×58mm Arisaka, as a sporting cartridge, is suitable for most big game with proper bullet selection.
7.7×58mm Type 92
The Type 92 (semi-rimmed) 7.7 mm (7.7×58mm SR) was a machine gun cartridge and was primarily used with the Type 92 heavy machine gun and the earlier Type 89 flexible and fixed air-cooled machine guns used on Japanese planes.
All Japanese ammunition used gilding metal jackets for the bullets on ball and the Pentaerythritol tetranitrate (PETN)-filled flat-tipped explosive incendiary, cupro-nickel jackets for tracer and phosphorus incendiary and a brass bullet with steel core for armor-piercing.
- Ball—lead core
- Tracer—lead core
- A.P.—hard steel core
- Incendiary—white phosphorus and lead
- H.E.—PETN and lead
Late war ammunition can still be encountered.
- TM 9-1985-4, Japanese Explosive Ordnance
- "The 7.7×58 Japanese Arisaka (7.7 mm Jap)" by Chuck Hawks
- "The 7.7 Arisaka" by Bob Forker for Guns & Ammo
- Japanese Ammunition 1880–1945 Part 1; Rifle, pistol and machine-gun ammunition up to 20mm by Ken Elks (2007)
- Modern Reloading Second Edition by Richard Lee (2003), page 487
- Honeycutt Jr., Fred L. and Anthony, F. Patt. Military Rifles of Japan. Fifth edition, 2006. Julin Books, U.S.A. ISBN 0-9623208-7-0.