...the terminal velocity of your typical bullet coming back down varies a lot but is normally more than 200 feet per second.Link
And, other writers on the subject (there have been quite a few) say that tests on cadavers show that skin is punctured and underlying organs messed up (my words, not theirs) at bullet velocities that exceed 180 feet per second. And, since falling bullets typically strike people in the head or shoulders, this appears to me to be a very dangerous practice.
Reader comment: David says: "I worked my way through much of my higher education as a night clerk in ER's, and every year at Xmas and the 4th of July there'd be a few falling gunshot wounds. I'd like to reiterate that the bullets are going more than fast enough to kill people when they hit the ground--there have been cases where a bullet punched through a car roof and hit someone inside. Moreover, the falling trajectory gives the bullet a much longer path through the human body than a flat trajectory, making the wounds much more gruesome than a typical gunshot, even if they don't hit the head or shoulders.
"Speaking as someone who's seen the results I can honestly say that shooting in the air is a Really Bad Thing. Really--don't."
Reader comment: Jamie of Slashdot says: "In their answers to the questions our Slashdot readers sent them, the Mythbusters team recently promised an interesting report on the 'bullets fired straight up' question...
What is your favorite Busted Myth and your favorite Confirmed one? ADAM SAVAGE -- I've always been partial to the Penny Drop myth, i.e. will a penny dropped from the Empire State Building kill you when it hits the ground? To me, that was one of the most elegant and simple applications of science to a question that we've done. Until last week. We just worked on a myth called "bullets fired up" -- i.e., will a bullet fired directly vertically kill you when it comes back down. We did tons of research on it, and in the end, added significantly to the body of knowledge that's out there on the subject. I won't give away the ending, but we nailed this one.
Reader comment: Ben says: "Despite every attempt to do so, I couldn't find an archived news story of the following very real tale (sorry). I know this might ring of a FOAF urban legend, but it's not! Trust me!
"In my hometown of Erie, PA, about 10-12 years ago, there was an incident just as described in your post. An adolescent girl was struck in the head with a falling bullet as she watched New Year's Eve fireworks...the irony of the situation was that she was attending on of those 'alcohol-free, family-friendly' New Year's Eve events, whereas the guy who shot the gun (who, incredibly, was eventually caught) was at a party a few blocks away.
"In the relatively crime-free location of Erie, where shootings are rare, this story was huge, and the criminal trial (as well as the girl's recovery) was followed by the media for weeks to come."