I know that in many interest areas other than shop tools WD-40 is a dirty word. For sure that is true WRT bicycles. I suspect also guns. It is often blamed for gunking up works. While it seems so fluid, most of it is solvent. When that is gone the detergent and lubricsting residues may or may not be good for fine gun works. Fair enough. I’m not suggesting to spray it all over the springs and other small parts inside guns and then let it evaporate. What I am proposing is to use it as a good cleaning fluid for the inside of barrels especially in shotguns and rifles. My 12 ga barrel stubbornly refuses to come completely clean no matter how many times I scrub the inside with Hoppe’s and swab it with countless patches. I’m wondering if the WD-40 wouldn’t work. It's highly detergent, cheap and easy to spray in copious quantities down the full length of the barrel. Assuming I swab it all out after, any reason you can see not to try it?