WOW, I have the same brown patches using BB just after a few minutes of sitting in the barreal. Most times after I clean the barrel I'll swab with BB, the run a dry patch, swab with BB, to make sure I coated it good, then swab with a dry patch and BB again. And during the dry patches I noticed they were brown. I figured I had'nt cleaned the barrel good enough, so back to cleaning. I inspected the barrel after cleaning and it was mirror clean. So back to the BB, and brown again after a patch or two. I jsu figured it was a chemical reaction to the metal and BB and nothing to worry about. But now you got me worrying and If I have to change what Im using I will. I did order 2 cans of the MontanaX and there on the way. I'll use that and see what happens. What did you coat your barreal with after the BB and befor the montanaX? Ron