Those are all really cool, especially the Cheytac M200(first one).
Gas guns can be temperamental, but thats only because in airsoft we use gasses that have to expand to the gas form.
-Propane is a gas that is normally used for heating. In its normal state it is a gas, but in airsoft we compress it to be used as a liquid. I couldent find the freezing point of propane but to give you a rough idea about how cold it is the boiling point of propane is -42*C, which for all of us Americans is approx -43*F(yea I tipple checked the math).
-Green gas is Propane that has some extra chemicals in it to make it expand better than normal.
-Co2 is not as widely used by airsoft but some clone handguns(WE mostly), use it as a alternative to red gas. Co2 closely resembles Propane in function, however the added pressure that is needed to use Co2 as a propellant is where the extra FPS comes from.
-Red Gas or HCFC-22 or Chlorodifluoromethane(clor-o-di-flu-or-meth-ane) is a common air conditioner gas, many of you would know it as Freon 22. I don't really know much about this gas except that it tears the crap out of seals and O-rings which causes many players to stay away from it. I have only seen it used once.
-Blue Gas or 134A gas as commonly known in airsoft is another chemical used in air conditioning. I'm pretty rusty as far as my knowledge goes on this gas. Its recommended with most Japanese GBB's. I used it for awhile but had to switch to green gas when it became unavailable because of the new air freight laws that were set in place. Its not as powerful as green gas(my results were about 30FPS less), but it is alot more reliable. It uses the same idea as propane and Co2(expanding).
Well thats all I know, if some of my facts are not right please anyone jump in with the correct answers. Also if anyone has used these gasses then jump in with your experiences with them. I looked at buying a Gas Sniper Rifle(Tanaka to be specific). But I got a
great deal on a TM VSR.
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