7.7x58SR Armor Piercing Core


Sometimes called the "Jap 31"
7.7x58mm Semi Rim brass case, brass encolsed steel core, no headstamp
For the type 92 and 97 Japanese machinegun. The type 92 could use both semi rimmed and rimmless ammo in 7.7x58mm. It is similar (except for the rim) to the .303 british, using the same .311 dia. bullets.


Dear Wolfgang:

Thanks for the excellent sectioned T92 7,7x58SR.

Just one Point: whilst the entire concept of a 7,7mm cartridge started with the 7,7x56R ( aka .303) after WW I ( 1920s), by 1929, the Japanese Army Airforce had developed the Semi-Rimmed 7,7x58R case with a 175-180 grain Bullet ( Type 89) which was used in Army Airfore Vickers (T89) and Nambu Flexible (T89 Flexible) Guns. The Semi-rimmed case was totally different and NOT interchangeable with the 7,7x56R, which was adopted by the IJNavy in 1927 (Type 87) for Vickers Aircooled guns in Naval Aircraft, and also Lewis Guns…in 1932, the Navy adopted their own manufacture Lewis Gun, with 97 round Magazines, for Small Boats, Aircraft and Anti-Aircraft use. The Cartridge was then standardised as Type 92 Navy (7,7x56R.)

At the same time, the Army required a heavier ground machine Gun to the old Type 3 (Taisho) 6,5mm gun, the original Nambu design improving on the 1897 and 1905 Hotchkiss guns. The new Gun would fire an improved version of the T89 ammunition, with a 200 grain bullet and increased charge, Semi rimmed case ( 7,7x58R).

At the same time, or shortly after, T92 Army ammo was also supplied to the Airforce for use in T89 guns as well. So by the time of entry of Japan into Formal war with China (1937) they had TWO “7,7” cartridges, not interchangeable with each other. ( T92 Navy 7.7x56R…Rimmed, head diameter .455" …Type 92 Army/Airforce, Semi-Rimmed, head diameter .475".

The only common item was the bullet diameter, .312" ( even the weights differed…Navy was 175 grain, Army 200 grain.

Then in 1939, after several years of experimentation following problems with 6,5mm ammo in China,the T99 cartridge, a Rimless version of the T92 Army was produced, and the T99 rifle built to use it.( original trial Rifles used the semi-rimmed T92 as is…it was found too powerful a cartridge for the short statured Japanese soldier, so the more “shootable” T99 grew out of these experiences.
Now full into WW II, the Japanese now had Three cartridges with a 7,7mm Projectile…one rimmed(Navy) one Semi-rimmed (ArmyMG,) and one Rimless (Army Rifle, LMG AND eventually MG.-- Type 1 “Woodpecker” Nambu–very few made).
The Rimless and Semi-Rimmed cartridges were interchangeable ( one way) ie, the rimless would chamber and fire and extract in a semi-rimmed MG, but NOT vice versa.

Strangely enough, the T99 rifle was not widely used in China at all, but was regularly found in the Pacific and Korea.
And after the War, Indonesia did make the three 7,7 cartridges interchangeable, by modifying the Type 99 rifle ( Bolt face ground out) to accomodate the semi-rim and the rim, as well as the rimless type of 7,7 Japanese ammo ( I have an Indonesian Modified T99…came directly to Australia from Indonesia in the 1980s). After Independance (1949) Indonesia had a Mixture of Japanese, Dutch, British and American Equipment.

Doc AV
AV Ballistics.


Doc AV’s posts are some of my favorite as they add a great deal of history that I have never seen in any of my other reading. Not just the technical specs, but the history and the context and often the weapons that used them as well.

Thanks, Doc!


This is an Armor Piercing cartridge, right?



AKMS: Yes, it’s an AP. In the coding scheme used by the Japanese army a black casemouth seal indicated AP; the brass jacket is a secondary identifier. Both the rimless and semi-rimmed 7.7 were produced in this version. Jack


Great history Doc AV. Thanks. It took 4 books to get my information above. You are a walking book of knowledge. Ever see/read “Fahrenheit 451”. And thanks Jack, couldn’t remember the word casemouth (brainfart), but black is AP and the red is incendiary.
Does anybody know whats the copmosition of the incendiary mixture? Have some, but don’t want to play with white phosphrous.


Be VERY careful. Not all incendiary is White Phosphourus and not all red tips indicate incendiary… If you are referring to Japanese red tips or red colored bands, these are not incendiary…

Be 1,000 % sure of what you are cutting into first. Ask here on this forum and you will get good, accurate information. WP is BAD stuff to run into…