Re: 10.7 MM
One of the Gentlemen on the other site researched the DRGM numbers and found it had to be applied for in 1905 as he found confirmed DRGM numbers for firearms built before and after that date.
The other stamps can range from 1893 till 1912 and felt it was more in the 1911 range.
Some other info from the other site
The proofmark for a choked rifle barrel was a "S" superimposed over the "W", under a crown. The 10.7 is not the cartridge the drilling is chambered for. Instead, it is the bore diameter(not groove or bullet diameter)of the barrel as measured by the proofhouse with "gauge rods"or pins.It means a 10.7mm rod would enter the barrel,but a 10.8 rod wouldn't.To determine the cartridge,it is intended for, better measurements will be required. The diameter of the head,length of case,at a minimum would be required.This is assuming your statement that it is a straight case is correct(it likely is).Your rough measurement of 2.5", for the length could fit a couple case lengths, depending on where the case stops and the leade starts and ends. It would also be nice to know the rim diameter and thickness(thickness can be indirectly measured by measuring the depth of the rim recess),as well as the groove diameter of the barrel.Since measuring inside diameters with a dial caliper can be from a couple to several thousanths "off", it is better to make a chamber cast and the measurements can be made from the outside.With these measurements, I'm sure we can find or make cases and bullets that will work.It is also likely we can ID the name of the cartridge, but that is not necessary to be able to shoot it. Just my guess is it is likely something on the order of 11x55-65R, but I could be wrong as I often am.BTW,even though you asked about a black powder load the steel jacketed bullet and GBP show it was a smokeless powder cartridge.
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