No clue if this documentation was used for the Japanese ammunitions but I stumbled upon it, I believe it is declassified as it wouldn’t make much sense to have it still classified but I DO NOT KNOW. I simply stumbled upon it nothing more and nothingness. Several other sites also are hosting this pdf documentation although the other ones are using older scanned copies of it.
One again, I do not know so I am innocent.
Anyway perhaps it will be useful for Japan, or perhaps it won’t I’m not even sure. Hopefully, Japan will improve in the shell department as many shells do suffer. Or are missing from the game? and honestly, some vehicles in-game would be pretty cool if they got those missing shells.