[L473ncy]

I think in some GBBR demos the mags had HPA (or CO2) lines attached to them. Could you do a similar kind of setup with some sort of one way check valve and pressure control valve to make it safe for GBB operation?

ie. You'd have a small 8 oz HPA tank + line leading up to your mag with pressure control valves to regulate pressure so your pistol doesn't blow up in your face. AFAIK HPA has no cool down whatsoever since it's pressureized air and doesn't need to change states and just expands compared to a liquid turning into a gas (endothermic "reaction").