I am curious because I have a wingmaster that prior to gun season, the bore was like a mirror, but after firing some slugs through it (it was a back up for my normal slug gun) it appears that right around the forcing cone the barrel metal is scuffed or something. I had just shot some trap with it a couple weeks ago and it cleaned up just find. I doesd the thing with bore cleaner so i am pretty sure it is not powder residue. Is this in any way harmful or could affect the gun?