People keep mistaking WD-40 as a lubercant, which it isn't. It was designed to protect against water and moisture. And there are lot better lubricants out there to use on your firearms. There are some oils in it from what I have heard, such as fish oil. But with the formula still locked away in a safe somewhere I don't know for sure. As for using it on a browned barrel or a oiled or stained stock, like anything that you use you should test it on a small area before you go all hog with it. On the primers being destroyed by it, that is one way to deactivate a primer. We used to just dump them in old motor oil but spraying WD-40 on them works just as well.