I was shooting my favorite target auto the other day and got caught in a downpour. Being a complete idiot, I continued shooting until I couldn't see the target through the scope any more. I then took the gun home and cleaned it throughly and let the stuff in my shooting box dry out. Next day, I find faint patches of rust on the outside of the barrel. It's unfinished, in the 1911 auto. This section of barrel was lubricated during the shooting, and it was less than an hour before I cleaned the barrel. I didn't notice the rust at the bench but did notice it under incandescent light later.
Be careful with water around your guns. I can't believe how quickly this did damage.
Fortunately, it's inconsequential in this case because a little bronze wool fixed it right up, but the message is still a serious one.