From WD-40's own website. One of the uses they mentioned was the slide mechanism on a pump shotgun. Also, the exterior where there might be spots of rust. Also, I only have a revolver, no semi-automatic.
Of course WD-40 doesn't want to run customers off. Notice they don't mention anyplace that is near anything in contact with ammo. THEY understand the meaning of wrongful death lawsuit and they also know that their product is a penetrant. Bottom line: You want to risk YOUR life by going on the cheap? How about the lives of your family?
Type of action makes no difference, the danger is the same for revolvers as it is for semiautos.