Have this old 8x57 Mauser that my dad brought home from the war. It is late war production and he started to sporterize it back in the 50's when I was a kid. He never finished getting it set up so it sat in his gun cabinet for years and when he passed I got it. It sat in my gunsafe for many years also til about 2 years ago I decided to get it shooting again.
First order of business was to shoot a couple of old factory rounds though it to make sure it didn't blow up. I tied it down on my shooting bench, tied a string to the trigger and got back about 20 feet behind a tree and yanked the string. So far, so good.
After that I finished the stock, got some decent sights on it, installed and after market trigger and worked up some mid level loads and it shoots pretty decent.
So yesterday I'm sitting at my loading bench and this old box of 8mm ammo is on the shelf and I notice it says 8mm(7.9) and I get my calipers out and sure enough, they mic .318! Just kind of rattled on down a .323 barrel!
No wonder they didn't show any pressure signs.

Better a .318 bullet in a .323 bore than the other way around!

Imagine how well it'll shoot when you start feeding it properly...

Keep us informed of the outcome. I doubt , knowing you to be a reloader , that you'll have any over pressure problems. I've had more fun reworking Mod 98s than any other rifle. Never had a problem that I myself didn't create. roger

Did the same with an 8x56 Mannlicher-Schoenauer and 220 grain Remington PSPCL's. Worked up a load using the old Powley Computer method, cut it back a few grains for starters and went out and shot a few. They went "Poof" rather than a sharp "Crack". Lots of carbon on the case necks. Then I noticed the bullets in the remaining rounds in the Case Guard had sunk into the cases. Measured the bullets and they all were .321" to .3214". Talk about fear of liability vis-a-vis .318" bores!