I'm not saying I totally buy the Myth Buster's explanation, and before watching it, I would have thought those celebratory rounds being fired pretty much straight up, would have had lethal consequences when they came down. After watching their demonstrations, I'm not so sure. It appeared that the bullets had very little penetrating power upon impact back down on earth. Apparently "terminal velocity", when you figure in air resistance, is much less than muzzle velocity.