Instructions
Press the following buttons in order if you are using the Default Southpaw Boxer controller layout: "X," "B," "RS" then "Down." "RS" means clicking the right stick, "Down" is the down button on the directional pad. The gun lowers out of view.
Enter this sequence if you are using the Bumper Jumper controller layout: "B," "A," "RS," then "Down." As above, "RS" means to click the right stick and "Down" refers to the down button on the directional pad. The player lowers his gun when the combination is entered correctly.
Use this sequence in conjunction with the Recon (Halo 3) layout: "RB," "X," "RS" then "Down." "RB" refers to the right bumper button, "RS" means to click the right stick and "Down" is the down button on the directional pad. The gun is lowered out of view when the code is entered correctly.