PTFE of lined valve is also used to coat certain types of hardened, armor-piercing bullet, so as to reduce the amount of wear on the firearm\'s rifling. These are often referred to as \"cop-killer\" bullets by virtue of PTFE\'s supposed ability to ease a bullet\'s passage through body armor. However, this is simply an urban myth as PTFE has no effect on a bullet\'s ability to penetrate soft body armor; its virtue is in the reduced damage to the rifling of the weapon from firing very hard ammunition (this provides the armor piercing capability). |