[Roundsworth]

Charlie, I really don't know what the real story is on the 'A' and 'B' shells. I went through my brass shells and found a 12B, but no 10B. I can still take photos to show the differences with the 12s. I recall reading a passage somewhere that stated that the inside diameter of the paper hull is the same as the inside diameter of the 'B' brass. So, maybe the bore of a 'B' gun is more along the lines of our modern, standardized bore, and the 'A' bore is/can be much larger.