[Mills]

I have a GH 12 gauge. When I look down the left barrel, there appears to be a shadowy area beyond the chamber which looks too clean to be pitting. On the outside of the barrels, however, there is no sign of any expansion. These are no. 2 frame 12 gauge barrels and are thick as culverts. I was just wondering if a bulge would show up inside the barrel but not outside or what this imperfection could be?