My old trade gun was made from an old .20 gauge 30" shotgun barrel I bought from Dixie years ago. Its bore was .625, and I shot .595 balls in it. With that gun I outshot a friends rifle on a trappers run, and won a ball split event against rifles. My current trade gun is an old Curly gun who's bore is .620, and length is 42". I shot it with the .595's, but couldn't get it to shoot like my old trader. I got a .590 mold from a friends estate and tried that, with the old patching I had used in the previous gun. The new combination is much better, not as good as the old gun, but better.
I did discover that Curly guns from back in the day, can vary widely, when it comes to bore diameter, and barrel contour, and should always be judged individually.
Hungry Horse