There's a thread in the HBO forum where mikeman445 pointed out a couple of tricks relating to weapon reloading in Halo; one that he was familiar with, the other he wasn't, but noticed in a tournament video featuring StK vs. TDT.

nof of ninjasonfire noted that StK discovered a bug where if you press the reload button twice and then switch weapons, the first weapon will reload its clip, thus bypassing the time needed to reload the weapon during the reload animations.

nof also points out that this trick still works in Halo PC, and is especially effective on the rocket launcher because of its long reload time.

It became known to nof about eight months ago, at which time he believes the knowledge was fairly exclusive. Guess it isn't any more. Here's hoping that Bungie and Gearbox can get this fixed in a future patch.