Some good answers in this thread, so I'll just add the trivia that a jet can fire its gun, and then maneuver in such a way that it shoots itself down with those same bullets. Ballistics is a funny thing. Here's the story:

In 1956, a Grumman test pilot was flying the F-11 Tiger fighter jet off the coast of Long Island. He dropped his nose 20 degrees, fired a brief four-second burst from his four Colt Mk.12 20-millimeter cannons, and entered a steeper descent before hitting the afterburners. A minute later, his windshield caved in and his engine failed. The pilot had assumed he had been the victim of a bird strike, but the accident investigation revealed that he had actually flown into his own stream of 20-millimeter cannon rounds. Although the rounds had a head start, they slowed quickly due to drag passing through the surrounding air. The rounds decelerated, the Tiger accelerated, and the two reunited in the sky with fatal consequences for the aircraft. The Tiger was totaled during the crash, and the pilot, while severely injured, was able to return to flight status less than six months later.