WD40 does have dryers in it, and it leaves behind a gummy oil substance that can clog up the works. It did so on a couple of modern guns of mine. I still have some of the stuff, but I use it on external parts only. I also use it to oil equipment that is used hard, like lawn mower wheels and axles, or weedeaters, etc. I have used it on large bladed brush cutters, and on my bush trimmer. These go through lots of oil, and I use the Spray WD40 on them when in use. When they are put away, for storage, I wipe the WD40 off, and replace it with a better oil for the pivot screws, and use the WD40 on the exterior surfaces as a rust preventive. As long as the tools are hung up in my garage which is heated, I have had no rust problems.
I cannot recommend WD40 as a internal gun parts oil, after my experience. I do know guys who are shooting several times a week, and the time between shooting their guns is so short that the WD40 does not have time to dry out. They spray the actions with more WD40 before they begin shooting, wipe the residue off and out of the gun when they are done, and then spray more WD40 on the gun to prevent rust, and lubricate the parts for the next couple of day. I began doing that, too, but then I had a change in my work schedule that drastically reduced my time to go shooting. When I got back to the range, several months had passed, and the WD40 had dried. I had not prepped the guns prior to going to the range, and I had left the WD40 in my garage! I blame myself as much as WD40. However, I have not experienced this problem using other oils, like Rem-oil, Tefloil, and others.
