With those dimensions sounds like my theory just blew out the window. With a .727" bore though, sounds as if that bbl has had a little honing. That size put's it well up into the 13/1 range. As I recall the word choke, the chamber marking, & the sub gauge sizes were all introduced in 1887. Thus after this date a bbl marked 13 should have fallen between .710" & .719", unless of course the stamper just goofed that day, a situation not unheard of.
Incidently have you checked position of the top lever with bbls detached. Many British & continental guns were seemingly not made with compensating bolts & the lever just always returns to center. On these guns the bolts were apparently simply made with a minimum clearance necessary for the bolt to slide home `& do not seem to wear much from there. I guess the increased friction of a "Wear compensating" bolt tends to induce that wear to compensate for.
