Kris, it's not automatic. Those AR-15s are semi-automatic. One trigger pull, one bullet. It's very difficult and expensive to own fully automatic weapons in the US. Close to impossible for most people.
The military versions aren't even automatic anymore. They do have a selectable 3-round burst, but they leave the full rock and roll to the SAW gunners and Heavy Machinegunners now. Just not practical in battle anymore. When I was in Basic Training in the military, I ahd an M-16A1 with full auto. I admit it was fun as hell. Especially with tracers.