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Post by Dallas on Oct 18, 2011 9:13:21 GMT -5
Miles, splain how. The evaporation pressure drops as the ambient temperature drives the temperature of the gas down. That pressure is directly correlated to FPS. Lower gas temperature means lower FPS. This is gas 101. So please, explain how that may not be the case? This is all in an unregulated system, what we use in airsoft. With a regulated system as in paintball, your pressure just needs to stay above whatever pressure your regulator allows. But since we don't use regulators (mostly), that's not really an issue. Oh, ok. So while cold gas may not be an issue for one gun, it would be for another depeneding on whether it has a regulator or not. |
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Post by Knief on Oct 18, 2011 10:46:38 GMT -5
Only sort of. Most airsoft guns don't use regulators because they use gas that is a low enough pressure that a regulator is unnecessary. Classic airsoft guns (and paintball guns) use regulators because they run on HPA, Nitrogen or CO2, all of which would shoot hot enough to be dangerous if unregulated. Shitty CO2 pistols have built in flow restrictors to keep them from shooting stupid fast. Just about any gun running on green gas/propane isn't going to have a regulator. The volume of gas released, the duration of the release and how it's directed is controlled by valves and the strike force from the firing pin rather than a regulator in airsoft guns. Look at it this way: We use gas in liquid form. It's in liquid form because it's pressurized, since we've squeezed a large volume of the gas into a small area. When you shoot your gun, you release some of that liquid and it evaporates immediately because it moves from a high pressure zone (your mag's reservoir) to a low pressure zone (the air in and around your gun). It's that release of pressure that propels the bb. But there's more at play than just volume in space when it comes to determining pressure. Temperature is the other major factor. The colder it is, the easier it is to turn a gas into a liquid. That is, it takes less pressure to keep gas below its condensation/evaporation point when it's cold out. This is just a factor of chemistry and physics. *Side note, water boils at a lower temperature in Denver than Ann Arbor because of the atmospheric pressure differential.* So when you shoot your gun in the cold, the mag is less pressurized than it is in warmer weather, meaning you have less pressure running through your gas system and propelling your bb. That means lower FPS. Before we move on, there's one more point to make. We compress gasses into liquids at their evaporation point and not much further. It's hard to compress a liquid beyond that point and it doesn't serve much purpose most of the time. And if you were to pressurize a liquid beyond it's evaporation point, as soon as you released some (like filling a gas mag from you propane tank), the pressure will drop down to the evaporation pressure to fill up the extra space anyway, and you won't see any results from the extra pressure. Let's put some arbitrary, hypothetical numbers to it. Let's pretend that we all use Gas X (  ) in our gun, and Gas X's evaporation point is 100 PSI at 80 degrees F (propane is something like 110 or 120 if memory serves). And let's say that our gun requires 60 PSI to operate. And we'll make one more assumption, for every 10 degrees F the temperature drops, the evaporation point of Gas X drops by 10 PSI. In reality, this relationship isn't going to be perfectly linear, but it does exist for every gas, but for hypothetical Gas X, we get to know what it is. So at 70 degrees F, Gas X becomes liquid at 90 PSI. At 60 degrees F, it's 80 PSI, at 50 degrees--70 PSI, and at 40 degrees it's down to 60 PSI. Below 40 degrees, Gas X doesn't put out enough pressure to cycle the gun, and we can't shoot anymore. Now, let's put a regulator on our hypothetical gun while still running Gas X. Lets say our regulator will only allow 80 PSI per shot. Now, our gun will only release gas 80 PSI even when the temperature is 80 degrees F outside and the gas is pressurized to 100 PSI in the magazine. But as soon as you drop below 60 degrees F, your regulator isn't doing anything because the gas in the gun is below 80 PSI. At 59 degrees F, your gas is pressurized at 79 PSI, and the regulator doesn't prevent any extra pressure from coming through because there is no extra pressure. At 50 degrees, the gas is still running at 70 PSI, and a at 40 degrees, it's still at 60 PSI. The regulator does nothing to prevent the negative effects of cold weather on Gas X in our gun. The reason why paintball guns use regulators is because the gas they use doesn't evaporate/condense at 100ish PSI, but at more like 1000 PSI. So they need to tune that down to a more reasonable amount. HPA and Nitrogen then are much stronger gasses than propane and duster gas when it comes to shooting things with them. Unregulated they would probably drive paintballs through drywall. That's the function of a regulator. As a result of the high evaporation/condensation point of the gasses (in terms of pressure, way low in terms of temperature), however, they remain over the necessary pressure to operate a paintball or airsoft gun even as the ambient temperature drops. That's because of the properties of the gasses, not because of the regulator. |
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Post by Mles on Oct 18, 2011 11:02:07 GMT -5
Even despite the cold, doesn't the valve release the same volume of gas?
Based on my experiences, I have been able to get one-three strong shots off a GBB in cold weather but then it just poops out. Those shots still had good power, but the magazine didn't last as long.
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Post by Knief on Oct 18, 2011 13:01:47 GMT -5
No, actually it releases a lot more gas per shot, but at a lower pressure. The valve is going to stay open longer because there's less internal pressure forcing it shut against the outside pressure and the force exerted from the firing pin/hammer/hammer spring. With less pressure in the mag, there isn't nearly as much push on the valve to close. It's still essentially a blink of the eye process (unless it locks open and vents all the gas, as is wont to happen in the cold), just a much slower blink allowing more gas to come out.
But that doesn't really matter because at that point, volume isn't very relevant. It could release the whole mag right into the blowback chamber, but if it released that gas with the pressure of heavy smoker's wheezy cough the bb wouldn't even make it out of the hop unit. The lower pressure means less push on the bb regardless of volume. And really, the volume of gas expelled by most GBBs on a single shot (in warm temperatures) is more than enough to drive the bb and the slide. It's like putting a Type 0 cylinder in a carbine length AEG. You've got more air blowing the bb than needed. The difference is, with a GBB the power all comes immediately as the gas explodes into the lower pressure zone and then disperses. In an AEG, you get more power at the end of the stroke when the piston is fastest. Hence ported cylinders to maximize piston speed and pressure before the bb has left the barrel.
AEGs also offer a great pressure analogy, though. Imagine two guns, both with the same cylinder volume (we'll call them Type 2s, M4 cylinders and barrel). One has a stock TM spring and the other has an M120. Despite both bbs being pushed by the same volume of air, obviously the M120 is going to drive the piston faster and exert more pressure. The M120 is analogous to say, an 80 degree day while the stock TM spring is more like a 50 degree day. But let's put a larger cylinder in the gun with the TM spring (and a longer barrel to match, so we're not wasting the energy). You've now got a Type 0 cylinder with more volume being pushed by a TM spring, while you only have a Type 2 cylinder being pushed by an M120. Does the gun with more volume shoot harder? Of course not, the M120 is still going to drive the piston harder. Same goes with gas guns releasing more gas in the cold.
Those 1-3 shots you got may have felt powerful, but if you chronoed them I promise they wouldn't measure up to your warm weather performance. That's just not the way that gas works. I mean, colder gas = lower power is demonstrated every time you rapid fire a GBB. That's what cool down is. The gas cools as you dump volume rapidly and doesn't have a chance to be warmed by the outside air. Thus, later shots in a long series are significantly lower velocity. Even on a double tap, your second shot will be a little slower. Just, not noticeably so without a chrono.
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Post by Dallas on Oct 18, 2011 13:43:32 GMT -5
The reason why paintball guns use regulators is because the gas they use doesn't evaporate/condense at 100ish PSI, but at more like 1000 PSI. So they need to tune that down to a more reasonable amount. HPA and Nitrogen then are much stronger gasses than propane and duster gas when it comes to shooting things with them. Unregulated they would probably drive paintballs through drywall. That's the function of a regulator. As a result of the high evaporation/condensation point of the gasses (in terms of pressure, way low in terms of temperature), however, they remain over the necessary pressure to operate a paintball or airsoft gun even as the ambient temperature drops. That's because of the properties of the gasses, not because of the regulator. Ah, ok. That makes more sense. And about unregulated paintball guns, they will do more than just punch through drywall. Applying a few to your hand will take you out of the sport for a few months and send you to the hospital for a hand cast, as an unfortunate testosterone headed idiot learned a year or so ago. |
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Post by rodrick on Oct 23, 2011 1:41:11 GMT -5
I hope this is not considered 'necro' but I found this video that I don't know how to take.
The video is from nightstalker1985 (GHK's youtube account?) showing off a CO2 mag being used on a GHK PDW. The mag seems to have been placed in a refrigerator and clocks in at 2.5 C. A look at google brought up this:
2.5 degree Celsius = 36.5 degree Fahrenheit
So, the mag, with gas inside, is chilled to 36.5 F, and put into the gun where it is then chrono'd out to around 105 m/s (meters per second) which translates out to around 350 FPS, then the video continues to show him dump (On full auto) a total of 52 rounds down range, and it still has gas left inside.
This brings me to a few conclusions:
1) CO2 may, in fact, be airsoft's solution to winter woes: IE, we can get out and play when the land is white. I have not done much research on how AEGs work in the winter, but I jump to the conclusion that it may be more dangerous seeing as the gears could rust from contact with the snow, but mostly how batteries are affected. Looking in the After Action Reports, on a game back in the month of February, there were many complaints of everyone running out of energy before the game was over. Again, don't quote me, but I have seen some weird stuff happen to batteries in the cold.
2) CO2 may finally have a use in Airsoft: IE, the days of Crossman cartridge only used by crazy kids with cheapo airsoft pistols is closing. Those flimsy airsoft pistols may be the solution to a proper side arm in winter, seeing as when the temperature drops, the CO2 won't shoot crazy hot (maybe CQB legal).
To drive this home, I plan to be purchasing a GBBR and do my own stress test with both Propane and CO2 Magazines, as to which one, I don't know seeing as their M14 and G39 series don't have magazines that can directly take CO2 cartridges.
Just posting my findings.
EDIT: Being the dumb American I am, I assumed everyone used the silly not metric system.
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Post by TheEnd on Oct 24, 2011 0:10:27 GMT -5
I can tell you what will happen with the Co2 mag on stock internals. It will beat the hell out of your firing pin to the point that it snaps, and it will put a ton of stress on the BCG which may or may not break others things (like the nozzle threads) depending on how well it's put together. That's what mine did. Chances are any tests you are going to run have already been done and posted here. If anyone is thinking about buying a GBBR browse around the Gasgun.info forums. |
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) in our gun, and Gas X's evaporation point is 100 PSI at 80 degrees F (propane is something like 110 or 120 if memory serves). And let's say that our gun requires 60 PSI to operate. And we'll make one more assumption, for every 10 degrees F the temperature drops, the evaporation point of Gas X drops by 10 PSI. In reality, this relationship isn't going to be perfectly linear, but it does exist for every gas, but for hypothetical Gas X, we get to know what it is. So at 70 degrees F, Gas X becomes liquid at 90 PSI. At 60 degrees F, it's 80 PSI, at 50 degrees--70 PSI, and at 40 degrees it's down to 60 PSI. Below 40 degrees, Gas X doesn't put out enough pressure to cycle the gun, and we can't shoot anymore.
