Zombie thread resurrection!
The .318/.323 myth has been around for decades and is wrong.
The old rounds were measured on the land. The new round was measured on the groove. The tolerance for both overlap from .315 to .325, as do the barrels.
It's not a bad idea to use lighter-loaded commercial ammo in an old rifle, but there was no such thing as "high pressure" or "low pressure" ammo when the Turks used these in WWI and WWII. There was "8mm." Allee samee.
I've been shooting Yugo and Romanian surplus 8mm in my S-bored Commissions and 1893 Turks for 23 years.
I'm still waiting for someone to show me a photo of the alleged explosions that rip a hole in the space-time continuum
On the COMMISSION RIFLE, the difference is the "S" marked barrels had the CHAMBER throat rebored to take ammo with thicker case walls to support jacketed spitzer rounds vs lead rounds. THAT is the difference. The bores are identical, except that some of the EARLY ones have shallower rifling that proved inadequate for lead thrown at that velocity and wouldn't grip it.