It changes every day. But for this gun (planned): stubby 16oz. CO2 w/ on/off and anti-siphon, something to cover the valve/foregrip, some custom milling I'll do myself, a halo b (yes, to counteract the chopping experienced by using a hopper that lets the blowback push balls up the feed tube, it's a problem) and a nicer ball detent to counteract the multi-feed problems that would occur with a force-fed hopper. And if i can manage it, a lever-switch microswitch.
Well, all upgrades are super-hack... you can drill in a trigger adjustment scew, you can make a ball detent out of duct tape that doesen't suck, you can custom mill the body with an exacto knife (hell yea).
50 dollars on Ebay for a true electropneumatic marker.
Let's be honest, it's not exactly high quality.
Alright, as I assume most people don't actually know how this gun works, I'll tell you. the thing on the bottom is actually a low pressue reg, similar to those on the front of autocockers, which controls the ram/solenoid pressure. The air going to the valve, which is the thing that looks like the foregrip vertically on the front, completely bypasses the reg on the bottomline. The solenoid in the grip frame controls the bolt movement, just like on an impulse/bushmaster. When the bolt comes forward, it hits an angled wedge-like piece of metal which pushes the valve pin (which is straight up), sending the air through the bolt to shoot the ball...crazy huh. Not a bad design, but if the build quality were better, it would be a very very nice marker. Oh, I almost forgot to mention about 1/2 of this marker is made from plastic, including the mainbody and the gripframe. Also, the solenoid works perfectly fine on CO2.
Excellent buy, true electro for under 75 dollars... who'd a thunk it? I personally love the lack in quality materials... makes personalization really easy, heh. If my team takes off, we're applying for zap sponsorship in hopes of them rebuilding the gun design with some dignity.