CO2 or green gas? And what the cold does to your gas pistol

CO2 or green gas? And what the cold does to your gas pistol

the question of co2 vs green gas airsoft comes down to one thing: pressure. and that one thing is the difference between a pistol that lasts years and a slide with a crack in it.

let me get the most important warning out of the way first, because i don't want to bury it at the bottom.

warning: CO2 in a replica that wasn't built for it

never use a CO2 magazine in a replica designed for green gas only.

the pressure difference is not small. green gas comes out at roughly 150 psi (about 10 bar) at room temperature, and propane, the main component of green gas, sits around 124 psi. CO2 at room temperature comes out at roughly 800 to 1200 psi, depending on temperature. that's a multiple, not a few percent.

what happens then: the slide gets thrown back with far more force than it's designed for. at the end of its travel the slide slams hard into the frame stop. on a plastic or zinc-alloy slide (many replicas are ZnAl, not steel) that means cracks, usually in the rails or the rear of the slide, or a broken frame. sometimes after one magazine, often after a few hundred rounds.

so:

• check the manual or the manufacturer site to see if your model is CO2-rated
• some models are sold in both a green gas and a CO2 version with different internal parts. same look, different guts
• a CO2 magazine that physically fits doesn't mean it's allowed
• green gas in a CO2 replica is usually not dangerous, just weak. the other way around is not

if in doubt: green gas. then nothing breaks.

what green gas actually is

green gas is propane with a bit of silicone oil in it. that's it. the oil is there to lubricate your O-rings and seals, and that matters more than you'd think.

some people run straight propane from a camping gas bottle with an adapter. that works and is a lot cheaper, but then you have to add the silicone oil yourself, otherwise your seals dry out. and check whether your field allows it, some organisations don't want camping gas bottles in the safe zone.

there's also "red gas" and "black gas", which is just green gas at a higher pressure. same warning: only use it if your replica is built for it.

CO2: when it does make sense

CO2 has real advantages:

• far less sensitive to cold. this is the big one for anyone playing in a cold, wet climate.
• harder blowback, more feel
• more consistent pressure through the magazine
• cartridges are compact and cheap per unit

downsides:

• only in replicas built for it
• more internal wear, even in suitable replicas
• cartridges are disposable
• when swapping a cartridge gas can escape, and it's cold enough to damage your skin. don't do it with bare hands around the valve

cold: the problem for anyone in a wet climate

this is where green gas lets you down, and it's the reason i wouldn't run a gas pistol as my primary in winter.

why it happens. the pressure of a liquefied gas depends on temperature. at 20 degrees C (68 F) propane has a certain vapour pressure. at 5 degrees C (41 F) it's much lower. less pressure means less energy to the BB and less energy for the blowback.

and it gets worse while you shoot. when gas evaporates from liquid it draws heat. your magazine cools down as you shoot. so the first shot from a warm magazine is fine, and after ten shots in quick succession you've got a cold magazine with too little pressure.

what you notice at low temperature:

• BBs don't reach as far
• the slide no longer travels fully back
• the slide no longer locks back on slide lock after the last shot
• eventually: the thing doesn't cycle at all anymore

around 10 degrees C (50 F) you start to notice it. below 5 degrees C (41 F) a green gas pistol gets genuinely unreliable.

what helps:

1. keep magazines warm. in an inside pocket, against your body. not in a pouch on the outside of your rig.
2. rotate. carry three or four magazines, use them in turn, let the emptied mags warm back up.
3. don't dump them fast. shooting calmly gives the magazine time to take on heat.
4. CO2 in winter, if your replica is built for it. that's the real fix.
5. hand warmers in the mag pouch. works better than you'd expect.
6. don't leave it in the car. a magazine that sat in a cold car all morning starts on the back foot.

warning the other way: don't leave filled magazines in full sun or a hot car. pressure rises with temperature, and the relief valves in magazines are there for a reason. a magazine leaking in the sun is the best-case scenario.

chrono and gas

because pressure varies with temperature, your speed varies too. a pistol that chronos fine in the morning at 8 degrees C (46 F) can shoot noticeably harder in the afternoon at 20 degrees C (68 F).

the limits are not a suggestion, and they vary by country and by site. build with margin. if you're sitting right on your field's limit on a cold morning, you'll be over it in the afternoon. get re-chronoed during the day if it warms up a lot, and always chrono to whatever your local field enforces.

so which one

green gas if:

• you play in summer and autumn
• your replica is built for green gas only (this is the most common case)
• you value consistency over power
• you want to keep your replica a long time

CO2 if:

• your replica is explicitly built for it
• you play in winter and want to make it work anyway
• you accept there's more wear

i run green gas most of the year and in winter i just grab my AEG. that's less romantic than hunting for a workaround, but it works.

Sources

• Elite Force: what is the difference between green gas and CO2
• Airsoft Station: difference between airsoft CO2 and green gas pistols

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Also on Airsoft-FOB

• also available in dutch: CO2 of green gas? En wat doet kou met je gaspistool