From wikipedia article
"Spring-piston guns have a practical upper limit of 1250 ft/s (380 m/s) for .177 cal (4.5 mm) pellets. Higher velocities cause unstable pellet flight and loss of accuracy. This is due to the shock wave generated as the super sonic pellet contacts the air. Shortly after leaving the barrel, the pellet falls below the speed of sound and the shock wave overtakes the pellet, causing it to tumble. Drag increases rapidly as pellets are pushed past the speed of sound, so it is generally better to increase pellet weight to keep velocities subsonic in high-powered guns. Sonic crack from the pellet as it moves with supersonic speed also makes the shot louder sometimes making it possible to be mistaken for firearm discharge and drawing unwanted attention. Many shooters have found that velocities in the 800?900 ft/s (240?270 m/s) range offer an ideal balance between power and pellet stability."
"In the 17th century, air guns, in calibers .30?.51, were used to hunt big game deer and wild boar. These air rifles were charged using a pump to fill an air reservoir and gave velocities from 650 to 1,000 feet per second (200?300 m/s). They were also used in warfare; the most famous example is the Girandoni Military Repeating Air rifle. "
Not talking about powder-operated fasteners here, but let's consider. As a previous poster pointed out, a nail gun can drive a (say) 10d nail through 3 inches of wood. You know what? in my younger and healthier days, I could take a framing hammer, and after a few setup taps, also drive a 10d nail through 3 inches of wood in a single hit, too.
So, it must stand to reason then, that if the nail gun can kill at a distance, I should be able to (with practice of course) toss that nail up in the air, strike it with my hammer as it falls, and propel it to a lethal hit with similar performance to the nail gun, right? What do you guys think? :) Somehow I don't think I'll be doing any hunting with hammer and nails any time soon...
(I have no idea where that poster got the 100 mph figure though, which comes to mere 150 or so feet per second, not a lot faster than what a good major league pitcher can do to a baseball. Even the most anemic modern pistol rounds move at more like 800 fps. Personally, I'd rather get hit with a nail at 150 mph than a baseball at 100)