Okay, here's how to put your gun down, like in RvB. Hold all of this for three seconds at the same time: LB, RB, A, Crouch, & Down on the D-pad. If you press up on the D-pad instead, you get a bunch of numbers and stuff, so if you accidentally do, just press all of that again, up instead of down on the D-pad.
Only works in the following: Campaign, Custom Games, Forge Only works on the following network: Local, System Link
I like it better in halo 2 too. one button and can be done in multiplayer. and you could do this kind of Laser Beams coming out of your eyes when you shoot a beam rifle while you have your gun down.
You can only do it on local play. But seriously, they should let you do it on xbl. They did it to prevent button glitches, but people are finding ways to do button glitches anyways. So it's a lose lose situation, might as well let us hold the gun down.