[Arizona Carolyn]

Myth Busters just did a segment on this -- if fired straight into the air they don't come down and kill.

[Rte66]

Yes, they do. Oh, so maybe not straight up, but they do come down and kill. That's a fact.

[ThePythonicCow]

I wouldn't think a bullet fired straight up would be very dangerous. If someone dropped a pebble out of an airplane and it hit you in the head, I'd imagine it would smart some. I doubt it would penetrate the skull or cause lethal damage.

That bullet fired straight up eventually comes to a stop, and then falls out of the sky, just like that pebble. It's fairly dense (made of lead or such), and fairly compact, so would have a nasty terminal velocity, more than most pebbles. But nothing like its muzzle velocity.