[Pick Axe]

Well, here you go:

[quote:935c1]When the pin hits the round, it ignites the powder inside the round. This explosion creates the gas pressure needed to push the bullet down and out the barrel at an extremely high velocity. A hole, called a gas port, is located within the barrel for the purpose of allowing some expanding gas to flow through the slot and ram a piston-like device back against the bolt. This action pushes the bolt behind the magazine and accomplishes two desired results: first, it extracts the used round by a process that unlocks the casing from the bolt, then expels the casing out of the ejection port. Second, as the gas escapes, the bolt slides back and picks up another round. The process occurs within a split second and repeats until the last round of the magazine is used. The barrel is lined with rifling, or a twisted scoring down the barrel, which puts a spin on the bullet when it exits the barrel. This improves the accuracy of the round and is comparable to the spiral that a quarterback puts on a football.[/quote:935c1]

found at [url:935c1]http://engrwp.usc.edu/illumin/article.php?articleID=65&page=3[/url:935c1]