I recently got a question about an 1891 Mauser and my scope mounting approach. I'm sharing this info with the brotherhood FWIW.

"Craig, I used the bases for a small-ring 'K' size Mauser, and had to shim the rear mount to get it high enough. The 1891 rear ring is in-between the sizes of the other small-rings and the large-rings. Actually it might have been easier to have used the bases for a large-ring and shimmed the front one, but I used what I had.

"I measured over a dozen Mausers of various types and recorded their front and rear ring heights, then calculated the delta(difference between them) for a comparison. I found the large-ring 1898 delta to be some 0.055" larger than the small-ring 1895-&-Swede delta, while the 1891 delta was only 0.035" larger. I would have expected the 1891s to be the same as the other small-rings, but they're very definitely different.

"In any case with the 1891 you'll have to either shim one ring or make custom bases."

I measured only Mausers that I knew hadn't been buffed; at least 3 examples each of 1891, 1894/96, 1893/95 and 1898 large-ring. In a nutshell, I found the large-ring 1898s to be remarkably consistent in both heights and deltas while all the rest tended to vary somewhat in either their front or rear heights; for instance the Swedes had front rings that were identical and larger than the other small-rings while their rear rings varied widely and thus produced wide deltas, and the 1891s varied widely in both heights but their deltas were almost identical to one another. Go figure.

Then I measured the mount bases I happened to have, about a half-dozen different manufacturers each for both the large-ring and small-ring actions. Again, the 1898 bases were almost identical in their deltas while all the small-ring deltas varied widely, some actually varied QUITE widely.

Bottom line, if it's a small ring then MEASURE!
Regards, Joe