resources.gif - 8711 Bytes

Gas Pressures.

I posted the following on my Blog on Arnie's Airsoft Forum in October 2006

The figures in the graphs are taken from NIST's website.

As everyone knows, the "power" of gas guns drops at different temperatures. the reason for this is that the "power" of the guns rely on the pressure of the gas being used.

Simply put, when the temp is higher, the gas expands more due to the atoms being more "excited", the pressure in the container (gas tank) goes up, and power increases. When the temp drops, the opposite takes place.

A common thread that arises on the forums is "Can my Wakahashi Beretta M92BP take Green gas safely?"

The answer is always "YES" and "No"...

Let's start with "NO" - No gas gun, especially a GBB can use any gas without causing wear - All metal, TM, whatever, if you want a pristine GBB in a year's time, just plain don't use it...

Certainly SOME GBBs seem to have less problem with higher pressure gasses (and that pretty much means all the Propane based ones, regardless of how they are branded - So, include Abbey Ultra, HFC Green, pure Propane and Ultrair gasses of all sorts!), but using these gasses in any gun will (as well as giving better FPS) increase the wear that they suffer.

Moving onto "YES" - Yes is true because gasses don't always behave the same. Ever wondered why American Eagle/Cybergun gas always used to come in Summer and Winter (Ultrair's Summer gas is scarily powerful, in my experience, which leads me to believe it's Propane based)? The reason is simple, gasses expand differently, giving different pressures at different ambient temperatures.

So, everyone pretty much accepts that pretty much any GBB will work safely on 134a gas at 70F (20C) - Look away now if you can't agree with that. You might hanker for more fps, but I've never encountered any gun which couldn't COPE with this.

Looking at the graph below, you will see that that really means that most GBBs are safe with 85 PSI of pressure.

Now, if you use a Propane based gas at the same temperature, you're actually upping the pressure to 125 PSI - Plenty of scope for increasing damage.

What happens though, if we look further down the scale to see when Propane produces 85 PSI?

See? Around 50F (10C), Propane is producing the same pressure that 134a produced at 70F (20C), so you are quite safe using Propane in pretty much any gun, IF THE AMBIENT TEMPERATURE IS 50F (10C).

Flipping that round, if your gun is happy with a little more pressure (say 100 PSI), then you can use Propane safely up to 65F (18C), at which point it would be prudent to use 134a.

All the macho talk of "Real men don't use 134a" and "I only use Green because I'm not a girl" is tongue in cheek. In reality, there are times when only a wild gambler would use green and plenty of times when even the guns with the worst reputation for fragility really NEED Propane!

My rule of thumb (No warranty implied or expressed and bear in mind I don't fire off hundreds of rounds at a go on a skirmish - Your gun is yours to look after!) is Green up to 20C is OK and anything over needs 134a.

Where parts are hard to find, I might stick to 134a at lower temps, but I have fired (supposedly fragile) all plastic guns at 30C with Propane, although I would NOT make a habit of it!

Back to the Resources page

Back to the Homepage