I just bought a used Single Six that was pretty dirty. I disassembled it and cleaned it and while doing this I noticed a strange ring in the center of the barrel that won't scrub out. I ran my hand over the outside and there is a very tiny barely discernible bulge in the barrel (took 5 mins and have to hold it just right to even notice it while running your hand very very very slow over it). I have shot the gun and it shoots just as good as my other Single Six, minute of pop can out to 25 yards or so, is there something I should worry about or just keep it and shoot it?