Ridge, rim, or shelf refers to what looks like a partial counter-bore in each chamber, with a slightly smaller diameter in the front than in the rear of the cylinder.

These were actually called Old Old Model Russians, since there were two succeeding models, Old Model Russian and New Model Russian. Dating these is beyond my capabilities, since the commercial guns were serial numbered in the same range as the Russian Contract guns. The Old Old Model Russian was manufactured from 1871 to 1874 and all should have stepped chambers as they were all using 44 Russian cartridge.

Nice to find these in original condition and not cut, caliber modified, or otherwise butchered. Hope your assembly numbers all match up. The right stock should have the serial number matching the one on the butt-frame.

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Gary
SWCA 2515