For years only Noma made ammo for this caliber and if you could find it, it was (censored word) expensive. Back then the only load data was seriously reduced and those of use that shot Arisaka rifles a lot had to do a lot on our own.
I gave away 3 boxes of new Norma brass (that I bought on close out) with the one Arisaka I sold a year or so back because I'd rather make my loads in resized military '06 cases. I'd love to find a few hundred matched head stamp mil surplus 06 cases from the 60's or later to make a big batch of Arisaka rounds from. I had a friend that went as far as making a jig to stamp 7.7 on these...
I still have 2 of these rifles but I don't shoot either of them enough...
Tony