thnxPLEASE read the HPA Q&A sticky so we don't have to answer the questions about the difference.
HPA is highly recommended on the ion, and if CO2 is used an anti-siphon tank is nearly mandatory. The use of a CO2 oriented reg like a palmer stab is also recommended.
Please use the search button and read the stickies first next time, this has been discussed ad-naseum and the answers to your questions are all in this forum...
it would work if it output 800psi when it expanded. but it doesn't or else somebody would have used it. same with propane.(the tippy C4 actualyl ignites the propane, it does not rely on its expansive properties)that would be freakin awsome....n20 in a pb gun....suped up gun