Question: why wd 40 is bad?
Answer: WD-40 is hygroscopic and will attract moisture to the firearm which will result in rust. Drive chains of any type - Because WD-40 isn't a lubricant, it really will not work well on drive chains of any type. Gears of any type - WD-40 doesn't have enough lubrication affect to be useful on any type of gearing.