Why it works: This glitch is caused by an error with reloading. Many of the glitches in this game such as BXR and
Auto reload are associated with reloading.
What it looks like: A correctly executed double shot will most typically fire two shots simultaneously but depending on how well it is timed, there may appear to be a space in between the two bursts. Despite this you may have performed it correctly. The give thing to look for in a correct double shot is if the gun reloads without showing the reload animation.
Uses: This is one of the most misunderstood techniques in Halo 2. Due to the excessive amount of montages on the internet less experienced halo players perceive that in order to be efficient with the double shot you must use it aggressively. MOST pro players don't though. Instead this is used as one of three things. 1) As a defensive move when taking cover in a BR battle. 2) When in a game and you are trying to kill someone running away from you you can try and double shot when they almost dead person is about to walk around a corner and you will other wise lose the kill. 3) When you are behind in a BR battle and you are forced to stay in the battle without any option of running. You may notice that most of these uses are defensive moves. While i know a few players who are efficient enough to aggressively use this in BR battles.
Other Techniques: When you are holding a secondary weapon you're limitations are greatly reduced. One of the problems with double shot as mentioned before is the fact that if performed correctly you are left defenseless for a short time. There is a way to get around this "sitting duck" state produced after a double shot. The purpose of the secondary is in order to cancel the reload produced by the double shot. After double shotting with a secondary you can quickly press Y and then Y. What this will do is allow you to continue shooting as if you never double shotted in the first place. The notation for this is RRX YY RRX YY RRX YY RRX. Using this technique one can quickly empty a BR clip.
Practice: In order to rpactice this technique go into split screen by yourself and go to Lockout. Using the pillars on top of glass you can pretend they re people and get used to doubleshotting.
Thats really all i can say about double shot.
There is a lot more to be said about this great technique but for beginner purposes there is enough information here to get you started
Player 2: Yeah I double shot (ed) the shit out of him!!!!