A pertinent question to ask as we approach New Years’ Eve. The answer is, as is so many things, “it’s complicated.” According to the Straight Dope, the answer is “it depends.”
When an object falls, there are two main forces on it — gravity, and air resistance. Air resistance depends on how fast something is moving, so the faster the bullet goes, the more air resistance. So at a certain point, the forces of gravity and air resistance are in balance, and the bullet falls at a constant speed (since you need a net force in order to accelerate, or increase your speed). That’s called terminal velocity.
So, is the terminal velocity of a bullet fast enough so it has enough energy to penetrate the skin? Snopes reports that, back in the 1960’s, the army determined that the energy in a 0.30 caliber bullet falling from the air was about half that needed to produce a disabling wound. Case closed? Not quite. For one, different bullets have different terminal velocities AND different bullets require different speeds to penetrate the skin.
This is the only “Mythbusters” Myth to be rated both “plausible, confirmed, and busted” at once. If the bullet is fired straight up, it tumbles and falls at terminal velocity, they write.
But that’s not how bullets are fired, most are fired at a shallow angle. That’s why, in most news reports of victims of falling bullets, the victim is pretty far from the shooter. If the bullet is shot at a shallow angle, it doesn’t tumble, and can pack a hefty wallop — much faster than terminal velocity.
Conclusion: If you’re stupid and shooting on New Year’s — at least use a protractor. Fire at a 90 degree angle to the ground. If you’re shooting at a shallow angle, you might kill someone.
Of course, we’d all be safe if people just stuck to the old tradition of firing shotguns with pellets. Birdshot doesn’t have good ballistics — the bullets don’t spin cleanly, thus achieving the high velocities of bullets. You’d just be showered with pellets, as if they were tossed in the air.
For the mathematically inclined, here is a detailed description by high school teacher Roy Mayeda:
As to the speed at which the bullet leaves the barrel (muzzle velocity), a REALLY SLOW bullet would do 500 mph (733 ft/s), like a light 38 Special target load or light 45 Auto. The little old 22 Long Rifle high-velocity (“normal”) averages around 1200 ft/s (818 mph). Typical 357 Magnum defense/police load leaves at about 1450 ft/s (988 mph), .30-06 Springfield at about 2900 ft/s (1977 mph), one of the new hot-rod varmint cartridges, the 204 Ruger has a factory load listed at 4225 ft/s (2880 mph). As a rule, mainly older, lower-powered cartridges fire bullets with subsonic speeds, though the best competition-type 22 rimfire (22 Long Rifle) cartridges are also subsonic — avoids bullet experiencing turbulence that a supersonic projectile would encounter as it dropped to subsonic speed. For maximum accuracy, it’s usually recommended to keep the projectile either supersonic or subsonic for the entire flight, rather than letting it drop through transition speeds.