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Post by Canto on Oct 10, 2004 21:42:57 GMT -5
I'm considering buying a gas gun, but with winter coming up fast I need to know if gas guns work well in the winter. I have heard that they do not perform well under colder temperatures.
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Post by Jacko on Oct 10, 2004 21:52:39 GMT -5
Unfortunately, they do not. The gas has to expand to properly cycle the gun, which it cannot do (Expand, that is) when the ambient temperature is too low. It'll stay in a semi-liquid form and provide little, if any, power. High pressurized air tanks made for paintball help remedy this problem, but they don't currently make any sort of tool that could be used to fill GBB mags from an HPA tank.
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Post by Point-Man on Oct 11, 2004 15:55:17 GMT -5
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Wilycyt
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Post by Wilycyt on Oct 11, 2004 16:38:10 GMT -5
from my limited understanding green gas is essentially propane but i could be wrong
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Post by xaos on Oct 11, 2004 17:06:24 GMT -5
Propane suffers from the same problems as any gas propellant during the wintertime.
Gas guns work because the air outside is warmer than the compressed gas, causing the gas to expand when released. If the air is colder, the gas doesn't expand as much, thus leading to less effectiveness as a propellant.
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C.Martin
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Post by C.Martin on Oct 11, 2004 18:50:49 GMT -5
Xoas is on the money.
Only gases like nitrogen(i think) would work decently in the snow. Because nitrogen can be stored at a much colder temp them most gases, and it turns to liquid at a extremly cold temp.
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Wilycyt
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Post by Wilycyt on Oct 11, 2004 19:20:19 GMT -5
wouldnt nitrogen also blow the seals on most gas guns due to the much higher pressure its stored at?
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Post by xaos on Oct 11, 2004 19:50:21 GMT -5
Whether or not Liquid Nitrogen would blow seals is moot. It'd destroy the operating mechanism of the gun by quick-freezing it...as soon as the gun cycled, it'd shatter. And, even if that didn't happen, the firer's hands would probably be instantly frostbitten.
Liquid Nitrogen would be very, very unsafe to use in an airsoft gun.
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Mite
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Post by Mite on Oct 11, 2004 19:51:37 GMT -5
Xaos -
Sorry to inform you the science is a little bit off on your post.
First, gas guns work simply because the gas inside the magazine is at higher pressure than the ambient air (quite a bit higher actually). So the potential energy of the gas pressure (think of gas pressure like a battery) is converted into kinetic energy that moves the BB down the barrel and cycles the slide.
The gas is shipped to you in some kind of a metal canister. The canister is an engineered item. It has engineering specifications relating to safe temperature ranges with a certain amount of gas in it. As the temperature of the canister goes up (usually due to ambient temperature increase) the pressure in the canister goes up. This is why pressurized canisters for a variety of products always warn about throwing them in a fire (if the canister gets hot enough the pressure inside will exceed the design specifications and it will explode to relieve the pressure). I honestly don't know if everything in the canister is gas or if it is two phase (some liquid, some gas/vapor). Either way, the pressure of the vapor component will be related to temperature via the Ideal Gas Law:
PV = mRT
Where: P - Pressure, V - Volume, m - Mass, R - Gas Constant, T - Temperature.
So, ambient temperature goes up (with volume/size of canister, and mass of gas remaining constant) you get higher pressures.
On cold days, the pressure in the canister is lower. So, you won't get as much gas pressure in your magazine. And your gun won't have enough potential energy to perform.
In theory on cold days, if you kept your gas canister warm, and devised a magazine heater to keep the gas in the magazine warm, your gun would work just fine.
If there the contents of the canister are two phase then it gets a lot more complicated with vapor pressures and all kinds of other crazy stuff.
Mite
<Edit>
Any compressed gas should be somewhat workable, but one factor I am sure has importance is the molecular weight/standard density of the gas. Nitrogen (N2) is a pretty light molecule when compared with even straight propane (C3H8). Nitrogen has a molecular weight of about 28, Propane is about 44. 134a is even heavier (about 102).
</edit>
<more editing> The whole temperature versus pressure thing is one reason why you sometimes have to let the mag warm up a bit after charging it to have it work right. During the first part of the fill the gas goes from the high pressure canister to the lower pressure of the magazine and it drops a lot of temperature. Towards the end of the fill the pressure in the magazine is nearly the same as the canister and this effect no longer occurs, but some of the gas has been cool. As that gas warms back up to ambient temperature the pressure in the magazine will increase.
sorry to bore anyone </edit>
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Post by xaos on Oct 11, 2004 19:53:47 GMT -5
Ah. My bad, Mite. Shows you how much of the science behind our equipment I know
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Post by Canto on Oct 11, 2004 20:45:34 GMT -5
What about CO2 guns? Although they are few in number. Any good CO2 guns out there?
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Post by xaos on Oct 11, 2004 20:47:42 GMT -5
...what part of "gas doesn't work well in winter" are you failing to understand?
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Post by Gestapo on Oct 11, 2004 20:59:10 GMT -5
Well, Co2 works a little bit better than green gas in the winter. They have the S&W .40, it comes with an adapter for little co2 things.
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Mite
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Post by Mite on Oct 11, 2004 21:08:45 GMT -5
I think the small CO2 cartridges might be at higher pressures compared to 134a or green gas. So that might extend the lower temperature that the gun will function at, but there will still be a "floor" temperature below which the gun just won't perform (unless you keep the gas vessel at 70-100F).
NBBs should have lower temperature limits than GBBs because you don't need gas energy to cycle that big slide. The gun performance will still deteriorate (lower BB exit velocities at lower temperatures).
Mite
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Post by Knief on Oct 11, 2004 22:52:32 GMT -5
one more not about your post dealing with liquid nitrogen, Xaos. Liquid nitrogen, while very very cold, will not instantly give a hand frostbite, and shouldn't shatter the internals of a slide. I've dealt with liquid nitrogen contacting skin a lot (once is too much, but I'm talking about dozens of occasions) and it takes a few seconds before it can really do any damage. The amount of time that a valve is open on a GBB is not nearly sufficient to cool down skin enough to induce frostbite. I would see the biggest problem coming from cracking the rubber seals on any valves it came into contact with, i.e. all of them. But the plastic of the slide and metal of the blowback chamber should be able to handle that kind of cold for such a short period of time.
Canto,
Every gas produces sufficient performance at a common temperature. Let's say that temperature is 85 degrees. It's a nice temp on an average summer day. So, GBBs are designed to operate at that temperature. Let's say then, that a GBB is designed to shoot 300 fps on an 85 degree day using CO2. When the temperature goes down, so does the velocity at which the gun is capable of shooting. Regardless of what gas you use, the gun is optimized for a certain temperature. When that temperature drops, the guns performance decreases with it.
The only thing that will make a difference in how much the performance drops as the temperature does is the mass of the gas. I don't remember enough about chem class to go much further with this, but Mite could probably chime in again with more specifics. Really, the point that I'm getting at is just that just because one gas is typically found at a higher pressure at the same temperature as another gas, it won't necessarily keep that higher pressure at a lower temperature. And, that the higher pressure gas will still lose pressure at lower temperatures. If that occurs at the same rate at which a lower pressure gas loses pressure, then the gun running on the higher pressured gas will lose performace comperable to the performance lost by the gun using lower pressure gas at the same temperature.
One last gas thing to tie the last few sentence together and then I swear I'm done.
Gas is pressurized when it's put into a can. Green gas isn't just naturally at 80 psi (or whatever it is in airsoft cans) and HFC 134a isn't just naturally at 60 psi (or again, whatever it is in airsoft cans).
[TANGENT]
What this means is one of two things. Either the matter in the can is all liquid and the amount of matter in the can cannot be increased because liquid doesn't like being pressurized like gas does, or they could put more gas into the can but don't because they know that the pressure will ruin the gun. I like the former idea though, because 134a found bottled for use in other applications is at the same pressure that airsoft 134a is. The bottlers of these other suppliers of 134a would only use the same pressure by either coincidence that the products like the same pressure (unlikely coincidence) or that is the maximum pressure that 134a can take as a liquid. All this is taking into account the maximum temperature they warn you not to exceed on the bottle. It's usually 120 degrees F. If you exceed that temperature (though likely a temperature higher than that. they'd put a lower temperature on the bottle for safety's sake), the pressure builds up too high from the liquid trying to pressurize and it blows the seal on the can.
[/TANGENT]
Anyway, if we take a sample of gas A and gas B at 85 degrees F, and gas A is pressurized at 400 psi, and gas b is pressurized at 80 psi, when the temperature drops, there is no telling what the pressures could be. Gas A's constant could be one that tells us that even a drop of 5 degrees could lower it's pressure by 100 psi, while gas B will only lose 1psi of pressure. Which gun will perform better at 80 degrees? The one that lost 1/4 of it's pressure, or the one that lost 1/80th of it's pressure? That is taking into account that each gun is optimized for use with the gas it's using, i.e., it shoots at say, 300 fps at 85 degrees with a gas of that pressure.
It's been too long since chemistry. I have a feeling that i screwed up a concept in here somewhere.
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