I agree, shoot it some with patched round balls and check the patches after each shot. If you're getting shredded or torn patches, then you definitely have burrs that will plague you. If they're minor tears to the patch, you may be able to smooth the barrel up with JB bore paste or similar compound and some good ol' elbow grease. Otherwise, you might want to consider your other option of having it bored to a larger caliber as you previously mentioned.

Without a good look at the entire bore, it appears from your pictures that someone may have attempted to use the wrong size jag and got it stuck close to the muzzle. In their attempt to remove it, they scored the bore leaving those circular lines. I had a friend who did that with T/C Treehawk barrel. Instead of asking for help, he elected to just "unscrew" it and left circular score marks like the ones in your pictures.

BPS