Hmmmm, well it is definitely not bored to .35-30 (a .357 bullet is a good bit wider than the case mouth).

Still haven't made it to town for a caliper battery lol.

I think .32 Winchester Special might be a good guess. I am still pretty dubious about that ring on the brass, though. frown

I guess I will see about fixing the left shotgun firing pin myself. Haven't taken it apart yet, but depending on what the right-hand one looks like maybe I can use it for measurements to turn a new one for the left barrel. Then I'll leave the chamber casting and any potential reaming for a real gunsmith...