No, you should not use WD-40 on a gun. It is not a cleaner. It is not a lubricant. It is not a protectant. In short, it is nothing you want on your gun and everything you don’t want on your gun. It may be tempting to use it because you’ve got it on hand, but it will cost you in the long run. Go buy yourself a bottle, can, or set of wipes of any of the gun oils listed above and use them instead. Do not, under any circumstances, use WD-40 on your gun.