I believe that you have a arisaka type 99. If it is a t99 it should be in caliber 7.7x58. If it is the t38 ( which I don't think this is ) it is a 6.5mm cartridge if I am not mistaken. If you plan on shooting this rifle, make sure that you clean the gun very well if you haven't already because you want every shot to be as accurate as possible because I believe that the 7.7 ammo goes for about $1 a round. I hope that helps. Cheers