It is possible, a long shot, but possible, that what you are seeing is the "crud" ring left by some powders when they are shot and not cleaned to a squeaky clean shine. I would run some Hoppes No. 9 soaked patches through it, and see if that reduces the amount of area where the problem is. Judging by the position of the area in question, you might get lucky and have it just be powder fowling. Put a soaked patch on your ramrod, and let it sit in that area for a few minutes, and hopefully that will loosen that junk up. If it is rust, I bet you can still get it down to a level where it is just as smooth as the rest of the barrel, especially with a stainless brush and some good up and down movement. Sorry to hear about your barrel, I gave my brother a real good ass chewing a couple weekends for the condition of his new Optima Pro, its just not ok to leave these guns when they are dirty, and hopefully now my bro knows that since his nice nickel finish is all pitted around the end of the barrel and breach area, and his breach plug was basically welded in place.