Introduction #

Not every bottle of Airsoft Green Gas is the same. As is common with so many things in our hobby, the manufacturers either do not specify the product properties at all (and just say something like “high pressure” or “works down to 5°C” or something similarity vague) or gives very low details (like the specify pressure but do not specify under which temperature it was measured, etc). This makes comparing different products very hard and means sometimes people looking for good performance are just overpaying.

The experiment #

For this experiment, I build a simple measurement device for measuring the pressure of the gas in a Green Gas bottle. It is made out of a manometer that is supposed to be used to measure the pressure of the oil in the car engine. It’s not terribly precise but for green gas, we don’t need great precision as just a few °C in temperature difference makes a huge difference on the actual pressure anyways. The pressure that the device reports is very repeatable and is well within the pressure I would expect on a given temperature but it is quite low resolution so expect about +/- 0.5 BAR error in the absolute values.

I have measured 3 different brands of green gas:

• WE 2x
• ProTech GreenGas
• Nuprol 4.0

I may add some more brands/types in the future but it may be tricky to be able to measure them at the same temperature as the ones presented, but we’ll see. The values for those 3 gases were measured in BARs and additionally converted to PSI. The values for the pure Propane are calculated for a given temperature, not measured.

Some theory #

It is well known that Green Gas is just Propane with a small addition of silicone oil and without the smell. Some people even use pure propane to run their replicas with much success. The often seen opinion is that this means that all brands are the same and there is no point paying more. As we’ll see, this is not the case as manufacturers do add some higher pressure gases to the mixture (like Ethane) to increase the pressure. It is also widely known that the pressure of the gas drops with the temperature but it is hard to find hard numbers for that.

The silicone oil is there mostly to make the seals happy (however the need for this is debatable) and should not affect the replica performance in any noticeable way. What does make a difference, though, is the pressure. Unlike CO2, the Green Gas is stored in a liquid form which has a big advantage of the pressure being stable as long as some liquefied gas is present in the container. This means, that as long temperature is the same, the pressure you get from the green gas does not depend on how much gas is in the container. Of course, rapid decompression of the gas cools it and temperature greatly affects the pressure but that’s another matter.

The results #

Conclusions #

All the tested gases had bigger pressure than pure Propane (which happens to have the same pressure as Nuprol 2.0, according to its manufacturer). The WE 2X was, however, less powerful than the cheaper ProTech gas and, of course, much less powerful than the Nuprol 4.0. The differences are the biggest at high temperatures, but as we approach 0°C, the differences become very small. It’s worth noting, however, that at ~6.5°C the Nuprol 4.0 has the same pressure as the ProTech or WE at around 20°C so you should expect similar performance and load your gun at those conditions. The ProTech pressure appears to be the same as the Nuprol 3.0 is supposed to be but comes at a much lower price point.