Originally Posted by
rodwha
I'm chalking this up to a lesson learned. No matter what clean it ASAP! If you won't have the time to clean it that day don't shoot it!
That's probably the best thing to do. In my case a delay in cleaning was not the cause of the brown patches as I cleaned it right after a range session. I believe it happened because I poured boiling hot water down the bore to flush it out and so the moisture would eveporate quickly. I believe that for some reason the boiling water caused a bad reaction with the metal. I can assure you I'll never do that again.