7.7×58mm Arisaka

Type 99 7.7 mm rimless
7.7×58mm Arisaka
Type	Rifle
Place of origin	Japan
Production history
Produced	1939–1945
Variants	Type 92 semi-rimmed 7.7 mm
Specifications
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
Ballistic performance
Bullet mass/type Velocity Energy 175 gr (11 g) (Ball) 2,440 ft/s (740 m/s) 2,313 ft·lbf (3,136 J)

Type 92 semi-rimmed 7.7 mm
Various Type 92 rounds
Type	Machine gun round
Place of origin	Japan
Service history
Used by	Japan
Wars	Second World War
Production history
Variants	Type 99 rimless 7.7 mm (Arisaka), Navy type 7.7 mm
Specifications
Case length	2.25 in (57 mm)
Overall length	3.14 in (80 mm)
Ballistic performance
Bullet mass/type Velocity Energy 202 gr (13 g) (Ball) 2,200 ft/s (670 m/s) 2,350 ft·lbf (3,190 J)
Source(s):

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 her 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 cartridge after seeing the effectiveness of the 8×57 IS heavy machine gun in action in China during 1937. Due to 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 can be produced by reforming .30-06 brass, or fire forming 7.92×57mm cases. Case heads derived from the .30-06 will be slightly undersized and will bulge slightly just ahead of the web on firing, while the 7.92×57mm derived cases will be slightly short. Normal cases of the correct dimensions will 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 a good starting point for load development, since the two cartridges are nearly identical in power and size.