Actually between 1875 & 1887 was the period of time a choke bore barrel was marked with a bore & muzzle diameter stamp. A typical mark would have been 11B/13M ( the / is the only way I have to denote a fractional marking). This was along with the Not For Ball stamp.
On a barrel so marked it would have been extremely inadvisable to use a ball made for a Cylinder bored 11 gauge, but one sized for a 13 gauge bore would be fine.
If the gun were cylinder bored then it would only carry one stamp for the bore & have neither the mark for the muzzle nor the Not For Ball mark. My old Birmingham proofed W Richards is so marked. It is definitely pre 1887 as it does not have the chamber mark. It is cylinder bore in both barrels & is only marked 14, though it has 12 gauge chambers. It is possible it was made prior to 1875, but I really do not think so.
Prior to the general acceptance of choke boring, I believe that most guns, even the breech loaders, were gauged at the muzzle by the proof houses.
