A little more info.

This is a screen shot of presumably the original chamber cast done by the previous owner/his gun smith with the measurements; it was included in the documentation with the gun. It does closely match my findings and I would be willing to attribute the small variances between my measurements and his to my cheap calipers.



At any rate I will be looking over British cartridges to be sure.

According to the rifle gauge table found below, the bore measurements I have taken are squarely withing the 9.3 range. To me it is looking more and more like what Raimey mentioned; the guy who marked the gauge wasn't feeling very good Monday morning lol.

http://www.germanguns.com/tech.html

But the information gathering is yet to be concluded!