I ran across this article describing some interesting Xbox 360 controller modifications. Replacing the controller buttons with ammo brass is apparently a popular thing to do. The author refers to the replacement buttons as "bullets." I doubt that using bullets would make very useable, and certainly uncomfortable, buttons.
Admittedly, I've played very little Xbox. There are simply too many buttons on the controller for me to track. My son does have a very nice custom controller with lighted buttons, so I'm not sure that this mod would stack up with that. However, we certainly have enough raw material to make our own attempt.