Act in Halo 2 with the battle rifle where you pull the right trigger once, pull it again and hold it, and then hit the X button. If done correctly, two bursts of the battle rifle will come out for six shots. This can be quite handy if you're behind a shot in a Battle Rifle duel. Takes some practice, but if you're good at it, it'll really give you an advantage.
He had the drop on me, but i spun around, got 2 bursts off, then double shotted his ass.