Thanks again. Birmingham proof 1868-1875, with bore 13 = .710" - .728"
No re-proof.

Possibly Bro. Helsley knows the identity of 'JT' and 'JK'? Tube maker? Barrel finisher?
This list ends in 1857
https://paperzz.com/doc/9021082/birmingham-gunmakers-list

Is there a list in Douglas Tate's "Birmingham Gunmakers"?