Is the AR-15A4 gas powered?

Answer 1

Here's what wikipedia has to say about the Armalite-15 Rifle:

"The mechanism of operation for the rifle is known as direct gas impingement. Gas is tapped from the barrel as the bullet moves past a gas port located under the rifle's front sight base. The gas rushes into the port and down a gas tube located above the barrel. The gas tube runs from the front site base into the AR-15's upper receiver. Here, the gas tube telescopes into a “gas key” which accepts the gas and funnels it into the bolt carrier. The movement of gas into the bolt carrier forces the bolt and carrier in opposite directions."