Near the end of the movie Rene Russo's character is shot with the "cop killer" bullets, but is saved by the fact that she's wearing 2 vests. A few minutes later, Mel (Riggs) shoots through a bulldozer's front plate with the same type of bullets. There is NO WAY that 2 armored vests (and, BTW, there's no way someone could wear 2 vests without it being REALLY obvious and having their movement hindered) would stop a bullet that can rip through a couple inches of solid steel.