It must be remembered that the Brits used a over powered 9mm to use in their SMGs. The Japanese may have done the same. Either way this could lead us to a 5-2-8 Para squad for Japan. I would underline all the values on this unit. P.S. Some of that British ammo came to America a few years back. Warnings were sent out with lot numbers saying not to shoot this stuff in a hand gun.
captured ammunition stocks would tend to disagree that anything other than a relatively meagre round was used. Given an inherent instability of design to handle projected recoil, it is doubtful any idea of using an overpowered round was seriously considered in any folding stock version.
I can see a use in SSRing in a
2-
2-
8 or
4-
4-
8 to represent such armed units of Falling Sparrow SNLF paratroops. ( If that is one can cite sufficient evidence that such units jumped at least partially armed with these in hand , rather than in weapons canisters. )
There is no evidence whatsoever I can locate at this time that there was ever an overpowered round in this calibre being mass manufactured for use in full automatic blowback action weapons.