On the subject of doubles with bad barrels. I have a friend who deals in doubles and he had a nice rifle come in I think it was a Armey/Navey in .303. The out side metal and wood were in nice condition but Some one had shot corrosive ammo in it and hadn’t cleaned it properly. You couldn’t keep 2 shots on the target at 50 yards. The ones that hit were key holing. The answer was to send it out and have it rebored to a larger caliber. I believe it was brought up to .375 flanged mag. I did see a target with 4 rounds in 1 ½ at 100 after it was complete.
This is a practice that has been going on since the early days when people would have their BP rifle freshened up by opening the bore a little and having a new ball or bullet mold made.
I wouldn’t hesitate to re bore a rifle that had bad barrels and was other wise structurally sound.
Bill