"WD-40 will damage your firearm"

God knows how this one started. But I can assert, categorically and from extensive personal experience, that it isn't true.

There are various things said about WD-40, a wonderful product that's been on the market for decades. People will tell you "...it gums up and will cause your firearm to jam..." (it won't); or that "...it will remove the blue from your firearm because blue is basically a form of rust and WD-40 is a rust remover..."

I've been using WD-40 on all my guns, especially my black powder guns, for 40 years, with never a hint of "gumming up" or "removing blue." My standard practice after cleaning (especially with soap and water, the best cleaner for black powder) is to spray WD-40 liberally in and on all parts of the gun. "WD" is alleged to be an abbreviation for "Water Displacer," and maybe it is. The formula for it seems to be a trade secret: there's no patent number on the cans so I can't look it up on the USPTO database. It may or may not be a rust remover but it certainly is a rust preventer. Squirting it down the barrel of a gun is a bit messy but it definitely, absolutely, prevents rust formation. How, I don't know. All I know is that WD-40 works. Without harm to the gun in any way.