M1924 Yugo Mauser ? Not a "24/47" ? An original M1924, in 90 % condition ??? I find that very hard to believe.
Even the original M1924's were barreled with 0.323 (7.92 x 57 IS) barrels, let alone the post-WW2 24/47's. So, whichever model the rifle actually is, a 0.318 barrel is VERY VERY unlikely.....unless someone re-barreled the rifle. IF it is actually a 90 %, original M1924.....with a 0.318 barrel.....you've got a real unicorn. Literally, a one in a million.
As for ammo, DO NOT shoot 0.323 (7.92 x 57 IS) ammo through a 0.318 barrel, unless a super-weak load ! Even then, I wouldn't do it, though many have. Much of the US available 8mm Mauser ammo is loaded lightly, though using 0.323 bullets, for this very reason (as well as the reason of old rifles, of varying condition). Even then, I would not do it. IF you do have a 0.318 barrel, shoot 0.318 bullets....which will probably mean handloads. I doubt that you'll find 0.318 ammo - and not many 0.318 bullets for reloading, at that.
There are some around, but not cheap or common.
One possibility you will have, in order to do this safely and properly, is to load CAST bullets. An oversized cast bullet can be used safely, or oversized bullets sized down to fit. You can buy 0.321" diameter cast bullets and load them in 8mm Mauser cases, to make a workable load. These would still have to be loaded light though, as the cast bullets can't take as much velocity as jacketed.