CS-6 Longshot, Maverick, the gatling-style bullpup rifle, and two broken buzzbee shotguns.
The Longshot has a sealed breech and removed air restricters, the bullpup rifle has removed air restricters, and the Maverick is just plain broken. No air pressure at all. I think the air compression chamber isn't sealing anymore.
Edit: the bullpup rifle is the "Firefly". I also want that Vulcan automatic gun and the Long Strike "sniper" rifle.