With the huge mix of materials in our guns, inert gasses are ideal. Or relitevly inert gasses that will phase change to be stored as a liquid. Storing gas as a liquid, rocks, figureatively speaking. It take something huge in volume and makes it tiny.
That's what make co2 so cool. And being stored ina liquid it's somewhat self regulating, so long as the tank maintains temprature. If you could come up with a way of making co2 maintain temprature, you'd have one heck of an airsystem.
Nitrogen, thankfully has big enough molucules not to leak quickly out of high pressure air tanks. Helium has been suggested before. But it will leak out of tanks, and may damage the tanks on the way. sorta how co2 soaks into black o-rings.
any other ideas are welcome. Inert is a good thing
To be an AGD supporter, one cannot be an AGD bigot. -Nero
Truth is a complex thing. One must govern by simplicity. -M. Mercier, special counsel to his Majesty for domestic matters. The Brotherhood of the Wolf
"You can't outrun Death forever, but you can make the bastard work for it."