Thanks, DM, for the insight on the 11 bore. That consideration hadnt crossed my mind.
Argo, thanks, for the proof marks chart.
And thanks, Miller, for the explanation of the letters in the mark and the Birmingham connection.
At least I now know that the gun could be of the period that would support the oral history. That is significant.
Lastly, anyone across the pond have any knowledge of W. Morse & Co. or resources you could check? My thanks to you for looking.

Speude Bradeos