If your Xbox controller lacks a certain something-something, you could try doing what this guy did: replacing the buttons with spent 9mm bullets.

Or you could just buy one off Etsy user DieselLaceDesign:

This is a new name brand factory Microsoft Xbox controller modified the ABXY with real fired 9mm bullet buttons. Everything functions properly and each controller is tested fully. Please specify when purchasing black, white or whatever other color Microsoft manufactures and is easily available for me to pick up at a local retailer.

Price: About $55

Note that if you just want the bullet buttons, or if you want a wireless controller, DieselLaceDesign will do that too.

-Set of 4 DIY bullet buttons w/ Xbox tamper proof screw driver $20 plus shipping
-Set of 4 bullet buttons w/ my installation on your controller $25 plus you cover any shipping
-Set of 4 bullet buttons w/ new Wireless Xbox brand controller & installation $90plus shipping

[Source]