I just reviewed a bunch of old UMC paper, and I don't find A and B shells mentioned in the 1860s or 70s, just that they make brass shells in 8 to 14 gauge and for Sturtevant, Orcutt or Berdan primers. A and B shells are mentioned in the 1880, 1882, 1884 and 1885-6 UMC catalogues. The 11-gauge shells are only listed in the 1880 and 1882 catalogues, with just the 2 3/8 inch 11 B in the 1882.
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