From http://www.straightdope.com/
"For further insight, we turn to Hatcher's Notebook (1962) by Major General Julian S. Hatcher, a U.S. Army ordnance expert. Hatcher described military tests with, among other things, a .30 caliber bullet weighing .021 pounds. Using a special rig, the testers shot the bullet straight into the air. It came down bottom (not point) first at what was later computed to be about 300 feet per second. "With the [.021 pound] bullet, this corresponds to an energy of 30 foot pounds," Hatcher wrote. "Previously, the army had decided that on the average an energy of 60 foot pounds is required to produce a disabling wound. Thus, service bullets returning from extreme heights cannot be considered lethal by this standard."
If 30 foot pounds doesn't mean much to you, the bullet made a mark about one-sixteenth of an inch deep in a soft pine board. About what you'd get giving it a good whack with a hammer. Note that we're talking about bullets shot straight up here. If the bullet is fired more or less horizontally, it may not lose much speed before returning to earth and could easily kill someone."

From another site.
"the terminal velocity of a bullet could be 300 or 400 feet per second. This could be about 300 miles per hour..
It's going about three times as fast as a professionally hit tennis serve"