The shotgun buttplate I think places it manufactured in Bridgeport CT. unless it's a Hartford, then that would be a special ordered rifle. The barrel stamps are the telling factor - Bridgeports are stamped "Old Reliable". The major dealers J.P. Lower and Son's, and Walter Cooper out of Bozeman MT, are the main two. The cartridge lengths were stamped seemingly at random in the day. S.A.A.M.I. where were you at the time
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Mike Venturino's book "Shooting Buffalo Rifles of the Old West" lists almost everything you need to know. As far as calibres go 2 1/10 - .45-70, 24/10 - .45-90, 2 6/10 - .45-100, and 2 7/8 - .45-110. The fabled .45-120 didn't exsit until after Sharps had closed its doors. Rumour has it that they did chamber a Borchardt for one bought by Winchester for developmental purposes. So it's not likely, unless some knob had the chamber run out to this brutally wasteful chambering. Get a chamber cast done to make sure it wasn't rechambered even from a .45 - 2 1/10 to 2 6 1/10 for example. You can toast a chamber pretty quick shooting too short of a round in it too. Get it papered, and I don't know where you would do that. Congratualations on your find.