Take a look at the bonus you get for your Call of Duty: Advanced Warfare pre-order.
The Advanced Arsenal pack includes the Bullet-Brass Exoskeleton and the Bullet-Brass EM1 Quantum. As far as we’ve seen these are just jazzier-looking versions of items already in the game, so are more for personalization than any tactical advantage.
Sledgehammer Games Co-Founder Michael Condrey seems to support that interpretation in the pack’s trailerwhen he says the Bullet-Brass exoskeleton will “make you the coolest-looking guy on the field.”
Condrey also says the EM1 Quantum, Bullet-Brass or regular version, is a directed energy weapon and a “brand new class for Call of Duty.” It uses a battery power and has unlimited ammo and no reload if you manage its battery and overheating correctly.