Are there any paintball guns that don't need CO2 or HPA or anything like that?

Answer 1

In general, no, there are no paintball guns that don't need CO2 or HPA or the like. You need some kind of compressed gas to propel the paintball and operate the mechanism that loads the next round. There are choices to be made, but all the guns operate on compressed gas of some kind. It takes energy to propel that paintball at a target, and the energy must come from somewhere. In conventional weapons, chemical energy in the powder superheats the gases of combustion, and blam! In a paintball gun, the compressor that compresses the gas into the tanks provides the energy to propel the paintball. This is the simple physics of it. Ask yourself where the energy will come from if the gun does not use compressed gas. There are performance issues that might arise with different gases. And there might be some gases or gas mixtures that are none too kind on the gun parts, depending on whose version of the facts you believe. In any case, the gas will have to be free of any particles or debris, or of any moisture. And you already know why.