These chamber and bore sizes are very confusing. I'll try and explain what I see in the stock books. Stock book #1 and 2 show under the "bore" column, 10A, 10B, 12A, 12B. It doesn't say anything about brass vs. paper shells. The last letter designation for "bore" size that I've found is S/N 4989. That's in the middle of 1875. After that it's just 10, 12, etc for bore sizes. I have found entries that state 12B/14 and 12A/11. I understand going down to a 14 bore size from a 12B but not going from a 12A to a larger 11 bore. Very confusing and I've read The Parker Story and it didn't help!
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