Why is Co2 not effective for automatic gas blowback?

Discussion in 'Gas Powered Guns' started by Dead_Christmas, Jul 25, 2021.

  1. Zoms101

    Zoms101 New Member

    Beavercreek Township
    I always assumed that propane was inferior to CO2 because when a GBB gun is fired rapidly, the cooling of the magazine and internals reduced gas pressure. I figured CO2, with its higher pressure, simply wouldn't care. If I'm understanding Guges correctly, the CO2 just liquifies once it gets too cold as opposed to the propane, which just loses pressure?

    Although, since CO2 is often stored at higher pressures, would it not make a better propellant for non-rapid fire gas guns (i.e. snipers)? Or are there sufficient propane alternatives (red gas, black gas, etc.)?

    "Propane and propane accessories!" -Hank Hill
    Last edited: Aug 3, 2021
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

    Your assumptions are incorrect.

    Here is an example, One pistol, two gases.

    CO2 loses 60+ fps from first to last shot. This is not due to the CO2 turning to a liquid, it is already a liquid in the jet at 12g and a gas. It is due to it turning to a solid and when in solid state...there is "no" gas thus the pressure drop when the mag is fired.

    Same GBB with Propane and a LP valve.

    There is a 10 fps consistency...unlike CO2 which was a steady decline.

    Propane does lose pressure when it gets cold. This is true of "all" gasses based on the Ideal Gas Law - PV=nRT.

    However, Propane maintains a gas pressure far lower than CO2 (exemplified by the graphs), you just have to use a LP valve to keep the pistol in its pressure operating range.

    As for being a better propellent, no. Airsoft guns in gas form and HPA form all run around 125psi. Why directly hook up a gas that is 6 times too powerful and use a soft metal restrictor disc to mitigate pressure...that is not an ideal situation.

    There are other gases, but the color label is wrong and frankly misconstrued by people on their power level.

    Back in the 1990s, all Airsoft guns ran on Freon.
    This is bad for the Ozone...so a ozone friendly "Green Gas" was substituted - HFC122, while still harmful to the ozone, it was less so...

    Then came ET of "Top" Gas, another refrigerant it came in white 1 Liter bottles:


    Or in 2.2 Liter Bottles ET-2200


    This is the original red gas, a refrigerant and it had more power over 122. (oh which I still have a few bottles...

    I have yet to find a HVAC specialist from the 1990s on Asian "ET" refrigerants and it's formula.

    There was never a "Black" gas and is a made up class of gas.

    Then in around 2004 a US Gas bottling company realized that propane is near the performance of HFC-122 and substituted that into the can. Since HFC-122 is on the slow ban list too...and propane was plentiful and not harming the ozone, it stuck.

    Today there are 7 "organic" gases for Airsoft use and blends of them.

    R-152, Refrigerant
    R-134A, Refrigerant
    Propane/R-600, Cooking fuel and Refrigerant
    Propene AKA Propylene - Welding/Torch Fuel
    Ethane - Welding/Torch Fuel
    Acetylene - Welding/Torch Fuel

    "Iso Butane" Blends - Brought to us by Nuprol

    All sold under the various colors or Top, Green, Red and Black and people mistaking them for the "colored" gasses.

    Remember there are no standards in Airsoft, other then to fleece the player base as often as they can...with marketing words like Professional and Competition Grade for cheaply made products.

    One persons Red Gas is another persons Green Gas....
    Last edited: Aug 4, 2021

  3. Zoms101

    Zoms101 New Member

    Beavercreek Township
    Thanks for the history lesson! That information is quite useful.
    aotsukisho likes this.
  4. Automobilie

    Automobilie Active Member

    AFAIK KJW/WE guns all use non-venting fill valves. Tokyo Marui and KWA/KSC (generally) do and will 'leak' while filling until liquid starts spritzing out. That indicates the mag is full, but if you put o-rings in the valve they don't vent and tend to not fill reliably (like KJW/WE mags).

    Venting fill valves let off some pressure in the mag, keeping it below the tank pressure and allowing it to keep pushing more liquid. Plug the vent and the pressure will equalize between mag and tank and stop filling.