Instructions
Enter a level or local multiplayer match. You cannot be participating in an Xbox Live match if you want the code to work. The code will only work on offline multiplayer matches.
Simultaneously press and hold the following button combination for three seconds: Right bumper, Left bumper, A button, Left stick, and D-pad down. If inputted properly, you will hear a sound and your weapon will be hidden.
Return your gun back in sight by throwing a grenade, using the melee action or shooting your weapon.