OK, I made a little bit of progress on this old girl today.
I was going to run out to visit a couple of friends which are near one of my shooting ranges and on a sudden whim I quickly grabbed this rifle and took an orphan .45-70 case to check the rim size compared to the chamber and extractor. Seemed a good fit so I wondered if it might actually have been altered to the .40-50 Sharps BN that it was listed to be chambered in?
I ran the .45-70 case through my .40-82 Winchester die, then through my .38/56 Winchester die at which point the case "plopped" into the chamber right up to the rim. So far so good and it seemed to be a reasonable fit.
I primed the case and loaded my usual fire-forming blank of shotgun powder, a 1/4 sheet of toilet tissue, yellow cornmeal up to the case mouth, and then another 1/4 sheet of toilet tissue to hold it all in place. I stopped by the range and quickly banged off the fire-forming round to see what would come out of the chamber. Hmmm ... some interesting results.
The case had a very "pregnant" bulge amidships, but showed a very distinct shoulder and neck. It looked rather familiar in shape, so when I got back home I quickly dug out a round of 11mm / .43 Mauser brass and compared them. The shoulder is at the same length and the "bulge" is about the same diameter as the .43 Mauser case, and the case mouths were about the same inside diameter.
I took a round of loaded .40-50 Sharps straight and the entire bullet AND case mouth dropped in at the muzzle. I took a factory loaded round of Dominion (CIL Canada) .43 Mauser and the bullet is a nice snug fit at the muzzle.
From the distinct line showing on the fire formed .45-70 case which appears to be the end of the chamber it would appear that this rifle is in some sort of 11mm based on the .43 Mauser case, with the shoulder at about the same length, but with a much shorter neck. (Overall length appears to be about 1.94".) I couldn't match it up to any of the 11mm cartridges in Donelly's book, so it is likely some gunsmith's proprietary 11mm cartridge of about 11.15x50mm. I'll definitely have to slug the barrel to determine actual groove size, and do a cerrosafe chamber cast to determine the exact case length.
For comparison here is the fire-formed .45-70 case, a .43 Mauser case, and a 9.5x47R case from one of my other Schuetzen rifles.
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