I'll tell you a little story of WD-40 and why I laugh at the "experts"... epically the the "I'm a gun smith" "types" that tell people they'll do harm by using WD-40 on their firearms. WD-40 does what it was MEANT to do well. It's a penetrating oil and "rust PREVENTATIVE".
Why do I laugh you ask. I put the shotgun I hunted with away for the off season. As I did every year after a thorough brake down and cleaning I sprayed it down with WD-40 and pout it in a zip-up case and put it in the closet. Yes I know now that was/is a no no. Did that every year for years and years, only this time it stayed in there for over 10 years. Poop happens! When I finally got around to taking it out I looked in horror as it appeared that my hunting partner of many many years was completely coated in rust. But wait! On closer inspection while it was dull brown it really didn't look like rust but rather some sort of dry coating. So I broke out some "WD-40" saturated a rag and wiped my old buddy down. Underneath the "dried coating of WD-40", which dissolved and wiped off immediately, was that shiny Blue Steal and spots of bear metal form years of work that I remember. WD-40 "PROTECTS and STOPS RUST". Is it a good lubricant? No! If it gets into trigger mechanism and doesn't get flushed out will it get gummy? Yep! Will it kill primers if you let it sit on your ammo? YEP! Does it disperse water/moisture and protect while stored? ABSOLUTELY! After hunting in the rain or taking a swim in the bottom of a boat my shotgun got a good spraying of WD to protect it until I got home and broke it down and clean it. NEVER A SPOT OF RUST!
So when the "EXPERTS" rant an rave about the horrors of using WD I just laugh. Over 40 years of using it on guns, the guns I've use it on work perfectly and don't have any rust.
Guns are not dangerous! People are! RKBA!