Mike
I am in the same position as you, no hands on the rifle, but interested and trying to be helpful.
What I have is a small collection of old hunting cartridges, so I can take measurements for reference .
Having rifle, reference cartridges and information all in one place would make things easier.
Raimey
I recently got some reprints of period (say 1900 to 1920) case catalogs: Utendörffer, Egestorff, Roth, DWM.
Besides the already discussed suspects (.450 Express or MB/Mauser base) I see no further hot candidates.
Without more and exact chamber dimensions my knowledge ends here.
My next idea to understand what the original chambering was would be to contact the Vienna proofhouse.
Alternatively, just to make the rifle shoot again with proper ammunition (you do not need to know the original cartridge designation for this) , to obtain exact bore and chamber dimensions and proceed as Mike proposed above.
Although .45-70 cartridges can be chambered, in my eyes this is not a .45-70 rifle.
Potentially dangerous with modern hot loads (+P or whatever they are called).
.45-70 cases will be signifantly undersize at the case head, I think you will see some "swelling" of the fired case below the rim - not as much as possible, but I assume this is luckily a modern case with thick walls at the case head.
Using old-type balloon head .45-70 cases possibly might result in split case heads.
That the rifle will not "regulate" properly with .45-70 cartridges is no surprise.
This depends on bullet weight, powder load etc., and one must try to find out these things.
fuhrmann
