The Gun Nut has put online a segment from Julian Hatcher's Notebook on guns (an invaluable source), dealing with what happens when a bullet is fired straight up.
The strange f/x duo in the popular Discovery Channel program "Mythbusters" actually did a segment on this, and while they were not able to measure the energy of a falling 30-06 round, they did approximate it and got about the same results as the Army study you mentioned, firing both 9mm pistol bullets (out of a 4 1/2" barrel) and 30-06 rounds out of a Garand. The rounds fell in soft, but thinly crusted-over mud on the CA desert somewhere up by Mono Lake, and penetrated 2 1/2" on the average for the rifle bullets AND the pistol bullets.
Their previous experiments in the lab indicated a much lower terminal velocity for falling bullets, around 150 mph, but even the Army's doubling of that speed could not result in skull penetration, only a breaking of the skin on the scalp at most.
The Mythbusters went farther than the Army though, and did some calculations about bullets fired "almost vertically". It seems that you don't have to get much more than five to ten degrees off vertical for there to be an entirely different outcome.
At those angles, the bullet describes a parabolic arc, and retains most of it's speed, and therefore more than enough energy to make a lethal penetration.
The Mythbusters surmise that all the confusion over this matter (the PhD physicist and blogger Wadcutter did the math for us two years ago) comes from what constitutes "vertical".
Celebratory gunfire is common in my area, which has a large Latino population. When I hear it, I seek shelter, because the chances are, these shots are NOT being fired vertically enough to be non-lethal when they come down.
Posted by: Rivrdog at May 11, 2007 08:31 AM