KC...

Great drilling! It may be in any number of 8mm variations, so a chamber casting is necessary. This maker was noted for propriatery cartridges and can present a bit of a problem to owners of his very fine firearms, accordingly.

There were some of these made in the original 88 version with the wide rim. I've found that the later 8X57JR ammo works just fine if the extractor catches even a bit of the rim. I had for a while a DR drilling in that early 8X57 chambering, and the later "J" bore rimmed ammo worked fine.

I would be willing to take odds that the rifle is an 8 X 72R Teschner-Collath variation...there were two, one with a narrower case than the other.

That gun says "Collath" all over it with the wing and the forend lever. The rifle barrel selector should be on the right front of the trigger guard. It is a beautiful and unique Classic.