Teach me about gas systems!

[Stuey]

So I was wondering if anyone could educate me about airsoft gun gas systems, mainly GBBs? I already know a fair bit but I'm looking for a good explanation of how positive and negative pressure systems work and the difference you can make by changing various parts. I hear you can alter fps output by cutting the floating valve for example? How does that work? How does the strength of the floating valve spring affect power? Does it affect gas efficiency?

 

Thanks! (who knows, maybe it'll make a useful sticky...)

[BaBaBooey]

Before we get into details, there are generally two popular types of gas blow back airsoft: HPA (high pressure air) and liquid charge. Again, generally, a GBB designed to run on HPA is designed differently than liquid charge, hence operates differently. But you can run a gun designed to run on liquid with HPA, and vice versa.

 

I'll over simply here, but HPA always remains as a gas...liquid charged is where the propellant is stored in a liquid form (the BB is propelled from the energy that is released when heat is applied to the liquid which makes it quickly turn to gas). HPA examples are Nitrogen, while liquid charged are Propane, HFC 134A, CO2, etc.

 

I assume you are wondering about the operation of the more popular liquid charged guns? Or both?

[Stuey]

I was after liquid charged stuff mainly yeah, cos that's what I've got! But if you (or anyone else) has any knowledge to dispense about HPA systems then, please, add to the thread!

 

I (and I'm sure many others) only know a small about BV systems, Sun Project, DaytonaGun and the likes. I know HPA has the advantage of being way more consistent and having almost no cooldown (almost none? None at all? How do the physics work I wonder...) because it's not stored as a liquid, but then also due to this requires very high pressures and (usually) external storage and regulation.

 

I wanted to make a tech thread about this because I think gas systems and how GBB etc. works is a bit of mystery to many...but I also know that some individuals understand a great deal about the mechanics of airsoft guns, so I wanted a place where they could help the masses to understand these things. It's only science/physics at the end of the day! Hopefully the information here will help me and the rest of Arnies to work how to best tune their gas guns for efficiency, blowback, fps etc.

[BaBaBooey]

I don't know of any BV that has blowback...these are typically non-blowback, full-auto (the semi autos came later on with, I think, the Asahi DVSCON), replicas. The main advantage of these types of guns is that they are extremely efficient since no gas is used to move a bolt/bolt carrier.  I have never used an Escort, DaytonaGun, Polar Star, etc...I do occasionally use my YE MP5 which I was told is essentially the fore father of these modern HPA blowback models. However, given that my YE is nearly 15 years old and I don't have any modern HPA guns, I won't comment too much about it. You can read more about the YE MP5 here.

 

A little about the "gas" we generally use. Again, the energy that pushes the BB is taken from the energy of the liquid changed into gas. Now what is generally needed to make a liquid to gas? When you make tea, you put the cold water over a stove so it can quickly boil. When water boils, we all know that its changing from liquid to gas. Same thing in airsoft, you need some kind of energy to make that change...usually heat. The more heat available, the more effective your gun. This is why I think most pistols are more effective liquid charged guns than rifles. The magazine is essentially held in the grip so, albeit very very small amount, there is some heat from the palm of your hand that can be used (again, it's probably a really tiny amount).

 

A common question at this point might be: which gas to use? Well it depends on how much heat you have. In the winter time when it's cold, you might be able to use propane on your stock plastic Marui pistol (requires less heat to boil). In the summer, when it's sweltering, you might want to switch to something as weak as computer duster (requires more heat to boil). A chrono is really important here...stock Marui pistols are designed to run at or below 1J. Test your pistols to determine the power it give using .25g bb's. Sometimes I need to run propane on my stock Marui P226R when it's very cold and it chrono's just below 1J...it's safe to use. This is why I think this thread is dangerous...just because Joe living in Antarctica can use propane safely on his Marui FN Five-Seven, doesn't mean Tim living in the Sahara desert can. This is why some players like to fill their magazines in the cold...there's not much heat that will turn the liquid into gas.

 

So lets start with probably the most important part of a liquid charged gun, the magazine. In order to keep the propellant a liquid, you either need to make it VERY cold or keep it under high pressure. Since its impossible to keep our environment extremely cold, the magazine keeps the propellant a liquid by maintaining a pressurized environment (think of your magazine as an airplane flying at 39K feet in the air...the air at that altitude is extremely thin so to keep a comfortable environment of nice breathable, thick, dense air, the airplane is kept under pressure). Any small leak in the magazine will instantly change the liquid into gas. 

 

So how much do we fill it? The tank of your magazine isn't really a vacuum...there's already air in there. So think of a sealed, solid container of air and we're going to jamb some liquid into it...if you think about it, it's very hard to do. You'll need a lot of force to press that liquid into a sealed solid container. That force and the air already in the tank helps generate the pressure needed to keep the liquid a liquid. There's only so much liquid we can put into that container before the container just blows up from all the pressure or there's so much pressure it can only go back into the source tank (this it NOT good). That (probably) won't happen because the source tank is also under pressure...it will naturally stop filling when the pressure between the source tank and the magazine equalizes (the seal at the fill valve is also not perfect so you'll always have some liquid leaking out that instantly turns into gas). Do I recommend testing this? No. I think, generally, a good 60 to 90 seconds is good enough. Also depends on how big the magazine tank is.

 

We also don't want to use our gun upside down, although some magazines (e.g. Western Arms) are designed so they can, but you do want to fill them upside down. When you flip the magazine over, all the liquid will end up at the top near the main valve. You don't want this, especially when the valve opens. You'll get liquid propellant into the chamber which is not good. You DO want to fill upside down, because it's naturally easier for the liquid to move from the source tank into the magazine...gravity I guess.

 

A popular magazine upgrade is the "high flow valve". In my opinion, most magazines do NOT need this upgrade. Unless your magazine valve is really poorly designed, it's already maximized to allow the most and safest amount of propellant out into the chamber. Let's take a cross section of a Marui P226 magazine...it kinda looks like this:

 

 

The valve knocker opens the main magazine valve at A...the pressure change instantly causes liquid to turn into gas at B. As long as the main valve is open, that gas will escape up into the chamber via the magazine gasket at C. This is what popular high flow valves look like (the stock Marui is the yellow one at the right):

 

 

There's less material around the body of the valve, so naturally more gas will move up right? Not really...the amount of gas that move out is controlled by how long the valve remains open. If you really want more gas out of the valve, you'll need a bigger diameter...NOT less material around the body. So with the high flow valve installed, the same section looks kind of like this:

 

 

Is that large opening really making an improvement? From my experience...none at all. Your mileage might vary.

 

Lesson two later on...

[Stuey]

I was about to say I already knew a fair bit of that but I'm not going to cos this would make a really good primer for people who don't know much about gas guns. Cheers Booey!

 

Couple of things...

 

You DO want to fill upside down, because it's naturally easier for the liquid to move from the source tank into the magazine...gravity I guess.

 

Exactly, it is gravity - the reason you fill upside is precisely so the liquid gas can flow into the magazine - it's denser than the gaseous gas in the source tank so falls to the bottom of the tank. You can only get a proper fill with the source tank upside down. If it's not, you'll get lots of gaseous gas in the magazine and much fewer shots as a result.

 

So how much do we fill it? The tank of your magazine isn't really a vacuum...there's already air in there. So think of a sealed, solid container of air and we're going to jamb some liquid into it...if you think about it, it's very hard to do. You'll need a lot of force to press that liquid into a sealed solid container. That force and the air already in the tank helps generate the pressure needed to keep the liquid a liquid. There's only so much liquid we can put into that container before the container just blows up from all the pressure or there's so much pressure it can only go back into the source tank (this it NOT good). That (probably) won't happen because the source tank is also under pressure...it will naturally stop filling when the pressure between the source tank and the magazine equalizes (the seal at the fill valve is also not perfect so you'll always have some liquid leaking out that instantly turns into gas). Do I recommend testing this? No. I think, generally, a good 60 to 90 seconds is good enough. Also depends on how big the magazine tank is.

 

You should fill GBB mags until either liquid starts to spill out (Tokyo Marui magazines, non silent-fill) or until you hear the gas flow stop (silent-fill magazines, e.g. KWA). At this point the pressure in the source tank and the magazine is the same, so gas stops flowing in either direction. The only way it can go is to an area of lower pressure - i.e. the atmosphere if it's not a silent-fill magazine. I'm pretty sure there's no danger to keeping the two connected however.

 

Test your pistols to determine the power it give using .25g bb's.

 

Any reason for .25s? Especially when .20g is pretty much the international standard for chronoing? (I know gas guns get noticeable power creep with heavier BBs, is that what you're getting at?)

 

I also quite agree with you about high flow valves - as far as I can tell they don't actually do anything on most GBBs and are a bit of a waste of money tbh. There are much better ways of increasing your fps.

 

Looking forward to lesson two!

[BaBaBooey]

Yes, I chrono with 0.25g's just to be a bit conservative. Marui does recommend to ONLY use BB's that are between 0.20 and 0.25.

 

A few more parts in how the magazine works. There is a significant difference between the design of the Marui and WA magazines...the WA M8045 on the right and Marui XDM on the left:

 

 

The WA has far more components, the most significant being the valve lock (part 509 on the M8045). Marui does NOT use valve locks on the magazine. In my opinion, the Marui is a better design.

 

Basically, the pistols are designed so that just enough gas travels out of the magzine to fire the BB at 1J and blow back the slide before the valve closes. From my experience, this is where Marui pistols excel...they seem to be timed so well that they are extremely efficient. Both pistols use something called a valve knocker lock to achieve this timing. Again, M8045 on the right and XDM on the left:

 

 

Part 118 on the M8045 and Part 52 on the XDM is knocker lock. The knocker lock is pressed down when the slide travels over it. On Marui pistols, when the knocker lock is pressed down, it will force the valve knocker to retract, allowing the valve to close. The WA model does not do this...it only moves the valve lock attached to the magazine so the valve can close using the spring inside it (the lock actually keeps the valve open). In my opinion, I think it's much more efficient to have the valve knocker retract than relying solely on the valve spring.

 

Another big difference is the natural state of the valve knocker between the two pistols. On Marui, the slide actually keeps the valve knocker lock in the down position with the knocker fully extended. Then why doesn't the magazine vent out when it's inserted? Marui knockers are designed to pivot up (VFC MP5A2 also uses this design)...when you insert the magazine with the hammer down, it actually forces the knocker to pivot up, keeping the valve closed. When the hammer is cocked back, the knocker retracts back into the chassis and then pivots back down, ready to open the valve. On WA, the natural state of the knocker is retracted...even when the hammer is down, it can allow the valve knocker to move back into the chassis by using the same pivot design used by Marui. Pull the hammer down and the knocker pivots back down, ready to open the valve when struck.

 

So if the movement of the slide actually controls the opening/closing of the magazine valve, what happens if you try and slow it down so the valve stays open longer? More gas out, more power right? A good way to slow down the movement is to A) use a stronger hammer spring, B. use a stronger recoil spring, C) use a heavier slide/bolt carrier, or D) some combination of A, B, and C. So now we've effectively slowed down the slide/bolt carrier changing the timing of the gun. I'll try to explain with more photos and drawings why this is NOT a good thing, especially stronger springs.

[NonEx]

Regarding filling the magazines, I just saw a thread on arms-cool that you should fill at a little over 45 degree angle and not 90 degree upside down. If you watch all of the "HK" pros in various HK shop videos when they gas up this is how they nornally do it. Not sure what the significant differense is but I think it might be that you don't overfill the magazine as easily this way?

[Stuey]

Regarding filling the magazines, I just saw a thread on arms-cool that you should fill at a little over 45 degree angle and not 90 degree upside down. If you watch all of the "HK" pros in various HK shop videos when they gas up this is how they nornally do it. Not sure what the significant differense is but I think it might be that you don't overfill the magazine as easily this way?

 

See, in theory it shouldn't be possible to overfill a magazine because the gas will simply flow until the pressures are equal. However it definitely doesn't appear to be that simple, there are definitely some weird shenanigans that go on depending on the relative sizes of the various containers...would love to fully understand the fluid mechanics going on in there.

[NonEx]

Well some manufacturers include information on approximately how many seconds you should charge a magazine, so I think there is something to it.

[Stuey]

Well exactly...let's think about this (I'm going to say this is propane as an example):

 

In theory the vapour pressure can't ever go above that of propane at whatever the ambient temperature is, and as far as I know it shouldn't matter what the liquid/gas ratio in a sealed container is, the vapour pressure will be the same. However, if you think about it the propane bottle is higher up than the magazine, so gravity will cause the hydrostatic (that the right term?) pressure of the liquid to be higher, allowing it to overcome the equal vapour pressure in the magazine, compressing what vapour gas is in it, causing the gas to re-condense back into a liquid and continuing to fill the magazine with liquid.

 

Could that be it? Or play a part?

 

Is it just me that really enjoys trying to get to the bottom of the science of the airsoft? There's so much bull*suitcase* science/misunderstanding of principles in airsoft...doesn't help that it originates in the Far East so a lot gets lost in translation or on the way over.

[NonEx]

Just a thought on the high flow valves. I've seen Bababoyes theory posted before. But doesn't the thinking in that assume that the limiting factor of the valve output is the opening inside the magazine and not the holes in the valve itself?

 

I guess that the flow of gas is higher from the opening inside the magazine than of those smaller holes in the actual valve.

 

It could be that on some models they are at a 1:1 ratio and thus a high flow valve does little to nothing.

 

But if the output of the gas is limited by the holes in the valve itself, then a high flow valve would do something.

[BaBaBooey]

Let me quantify my analysis, saying that it is limited to only the Marui P226R and E2.

 

Yes, the opening in the stock Marui valve is made to the exact size of the opening machined into the magazine so even if you made the body bigger, it does nothing. It's already optimized...however, if the opening in the magazine is much larger than the opening of the valve, then a high flow valve might allow a more efficient flow.

 

However, in my opinion, the only way to increase flow from a valve is to increase the cross sectional diameter of the valve (e.g. water flowing through a thin drinking straw vs. water flowing through a fire hose) or having it open deeper (e.g. the faucet in your kitchen sink...twist it open more and water flows out stronger and faster). Unfortunately, magazine valves usually don't work like the valve in a standard water faucet...unless something is damaged, it already opens up as much as it can when struck by the valve knocker.

 

I'll try to show how/why magazine upgrades usually don't do very much of anything.

[PureSilver]

There's only so much liquid we can put into that container before the container just blows up from all the pressure or there's so much pressure it can only go back into the source tank (this it NOT good). That (probably) won't happen because the source tank is also under pressure...it will naturally stop filling when the pressure between the source tank and the magazine equalizes (the seal at the fill valve is also not perfect so you'll always have some liquid leaking out that instantly turns into gas).

 

This is somewhat semantics, but it's not possible to 'overfill' a magazine per se any more than it's possible to overfill a cup of water. Fluid magazines aren't like HPA tanks where there's a safe amount of gas that can be forced inside before the internal pressure rises too high; you can pour as much propane as you like into an airsoft magazine and when it's full it'll just start spilling over like water from a full cup. So it's not possible for the magazine to 'explode' at all unless you heat it so excessively that the vapour pressure exceeds the strength of the magazine and you block all the valves (which are the design point of failures/blowoff valves).

 

There's also no downside to allowing gas to flow backwards and forwards between the bottle and the magazine - in fact, if magazines could get a halfway decent seal on the filler neck what would happen as you filled the magazine is some of the warm gas in the magazine would bubble back up into the bottle as liquid flowed down to replace it. Instead it's just allowed to escape (the hissing noise during filling), which is deeply wasteful, because it's faster to fill the magazine by letting the gas escape (so there's no pressure to impede the liquid flowing into the magazine) than it is to wait for the slowly increasing pressure to turn the gas back into liquid. So called 'silent-fill' valves don't allow the gas in the magazine to escape, but I'm guessing that the pressure of the liquid pouring into the magazine means that the gas doesn't bubble up into the bottle but instead just cools down and turns back into liquid as the pressure rises - either way, it's much less wasteful but a little slower.

 

When manufacturers say "only fill for X seconds" they're not worried about you 'overfilling' the magazine and damaging it, they're worried about it being so full that liquid sits very close to the top and escapes into the blowback unit when the gun is fired. When the gun is fired, fluid escapes from the top of the magazine. It's intended that what escapes is gas from the so-called 'vapour space' above the liquid. However, propane (and other airsoft fluids) have high thermal expansion ratios, so they expand significantly when heated. Therefore if you fill a cold magazine completely, as it warms back up it the expansion of the fluid causes it to reach equilbrium with the liquid level close to the top of the magazine, which is where the main valves are. Therefore, when you fire the gun, it's possible for a small amount of liquid to escape and enter the blowback unit before it has time to turn to gas - and that can freeze up the inside of your gun temporarily and cause permanent damage ('thermal shock') as parts (silicone parts like seals and routers being especially vulnerable) contract rapidly.

 

Is it just me that really enjoys trying to get to the bottom of the science of the airsoft? There's so much bull*suitcase* science/misunderstanding of principles in airsoft...doesn't help that it originates in the Far East so a lot gets lost in translation or on the way over.

 

Nope, it's one of the best parts. Remember that one of the reasons there's so much in airsoft is because it's in the manufacturers' interest to keep you ignorant. Green gas is a good example of this - gas chromatography demonstrated years ago that it's just propane with silicone oil. Now people buy propane in bulk from Colemans and it's a third of the price or less than 'special magic airsoft' propane.

[BaBaBooey]

Yes, I 100% agree that the likelihood of a magazine exploding from normal filling is zero. I was told that back flow should never occur since the source tank is generally much larger than the tank in the magazine. So if you do get back flow (which I think is also unlikely...and I do agree that it will probably vent out before moving back into the source tank), there is something very wrong.

 

Also, I was told that over filling a magazine is typically impossible to do. There needs to be a certain amount of air inside the magazine to maintain pressure to keep the propellant in liquid form. I don't think I have ever had so much liquid inside a magazine to the point where liquid is shot into the chamber from over fill. Impossible, no...likely, I don't know? From my experience, liquid propellant entering the chamber usually happens due to damaged components or unnecessary upgrades.

 

Bottom line here is that I don't think you can over fill a magazine? When I did have the rare chance to speak with a Marui rep, how long to fill was one of my main questions. They told tell me that a 60 to 90 second charge is typically sufficient. They do NOT officially have a recommended time..."officially" they told me that the magazine is full when propellant starts to vaporize instead of going into the fill valve.

 

 
Remember that one of the reasons there's so much ###### in airsoft is because it's in the manufacturers' interest to keep you ignorant.

 

I've been out of the business of manufacturing a LONG time, but from my experience, the average consumer is also content on remaining ignorant (I'm guilty of this as well...I don't care too much on how my car runs or how my smart phone works...yes, it's probably not good, but I'm trying to learn the basics). Most people came in to have their guns for repair and didn't care how it's done...also the guns were not as elaborate as they are now. As long their gun was shooting at their expectations for a reasonable price, they were satisfied. Now I'm not sure how things work outside of Japan, but if someone came in and asked questions, I would be more than happy to talk with them.

[renegadecow]

Well some manufacturers include information on approximately how many seconds you should charge a magazine

That's there for the impatient.

[renegadecow]

How do the physics work I wonder...) because it's not stored as a liquid, but then also due to this requires very high pressures and (usually) external storage and regulation.

You'd have to go into stereochemistry to explain that in depth and am sure will bore the brains out of 99% of your readers in the attempt. In laymans terms, HPA which is primarily made up of very small nitrogen molecules require a great heap of pressure to transition into a liquid phase. But you don't necessarily need to force it into liquid (in the case of airsoft/paintball use) because it holds enough juice to keep you going for a long while with a moderately high pressure. On the other hand, liquid propellants such as 134a and propane have huge organic molecules. They require less pressure for a phase change, but in doing so become extremely more efficient as you can effectively store more of it with a pressure ceiling. The down side to it, as BabaBooey already mentioned, is that phase change requires energy and draws it from heat. The more is spent by releasing pressure, the colder it gets (the principles of "cool-down" effect) and the colder it gets the less efficient it is for the liquid propellant to transition into gaseous form leading to waste and ultimately pressure drop and gun output inconsistency. The only ways to dampen the effects of cool down is by enlarging the gas tank, having a booster tank (allowing the now cold propellant extra time to warm up), physically heating the tanks with body heat or artificial means, or making the system more efficient by require less gas per shot to operate i.e. a lighter slide/bolt, shorter bolt travel etc.

[PureSilver]

I was told that back flow should never occur since the source tank is generally much larger than the tank in the magazine. So if you do get back flow (which I think is also unlikely...and I do agree that it will probably vent out before moving back into the source tank), there is something very wrong.

 

It doesn't matter which is larger, really, it just matters which is at a higher pressure. For example, if you turned the magazine/bottle the right way up during filling, the liquid fluid (being heavier than the gas) would obey gravity and drain back out of the magazine into the bottle. Or if you took a full magazine and attached an empty bottle to it, the pressure would equalise between them which would involve gas moving from the magazine into the empty bottle until they were equally full of gas (with liquid remaining in whichever was positioned lower). With current systems, fluid moving back into the bottle isn't a good thing or a bad thing. If valves were redesigned to be two-part so that gas from the magazine could be piped up to the bottom (now the 'top' of the inverted gas bottle) as it was displaced by the liquid flowing in from the bottle, it would allow much faster and less wasteful filling.

 

There needs to be a certain amount of air inside the magazine to maintain pressure to keep the propellant in liquid form. I don't think I have ever had so much liquid inside a magazine to the point where liquid is shot into the chamber from over fill. Impossible, no...likely, I don't know?

There doesn't need to be a vapour space but I agree that it's pretty hard to completely fill a magazine with liquid. The reason you don't see liquid propane spurting out of the magazine when it's full is that as it escapes it suddenly reaches atmospheric pressure and nearly instantly boils into a gas - so you only get momentary sensations of burning blobs of cold as they land on your skin. However, it must be possible for it to happen as that's exactly the reason that commercial gas systems are required to leave a vapour space when filling bottles - otherwise, thermal expansion can push liquid propane into the equipment the bottle is connected to (which in this case would be the BBU).

 

*Science*

 

That's pretty much exactly how it is - and it is bloody difficult to explain adiabatic cooling etc without using analogies that usually just confuse the situation. I might make a YouTube channel over the summer and try to do some explanatory videos with animations and props to better explain the principles of airsoft - it's not just gas, it's batteries, hop-up, muzzle energy, motor wiring, AoE; everything seems to be someone's blind spot!

[DEVILHUNTER]

Well, I'm not very good explaining this kind of science in English, since it's not my mother lenguage, but I will try to do my best.

 

I have been studing how the gas works since I bought my first GBBR, 4 or 5 years ago, and trying to the get the best performance with it (and the others I have now) with several gases (propane, R-410a and liquified CO2 from paintball bottles now). At the same time, I was studing thermodinamics on my college, so I have learned and understood some many thing about gas in gas guns.

 

All of you had done a great job explaining all to the people in this topic, but there are some little thing that I want to punctualize or I'm not in accordance.

 

In a liquified mag, there must be always liquid and gas. When you shot, the gas in pressure expands, and give us the power to our guns. This expansion is much faster that the time that takes the liquid to get in gas, so a small portion of liquid is converted to gas when the valve is open. Overfilling a magazine is impossible on most of the magazines, because the filling valve is not on the surface of the wall in the bottom of the mag, its deeper, so in this area between the bottom of the fill valve and the wall of the mag there will be always gas (unless you push really really strong the liquid into the mag).

 

Imagine a mag that we could fill completely with liquid. Once totally filled, we heat the mag so the liquid dilate. In this case, the hidraulic pressure will be much higher than vapor pressure, this is the hazardous situation. The mag could break, but before this happens, some seal of the mag will probably blow and release the pressure, so a mag explosion with a lot of sharpnel is a rare event. As you had said, in HPA this is possible, and some HPA low quality bottles have been exploded in piantball use.

 

Why have we cooldonw? Well, when we shot, the gas portion in a liquified mag, expands. In this expansion, the gas gets cooler, but this is almost irrelevant. What is not irrelevant is the energy (heat) that the liquid need to get into gas. So when we release the gas and need liquid to get into gas and rease the vapor pressure, the liquid take the heat of the other liquid and the metal of the mag. Now, the mag and the liquid temperature had down a bit, so the vapor pressure is a bit smaller, and we will need a bit more of gas to shot. So this new shot will waste more gas, so more liquid need to get into a gas and a bit more heat is need. This happens every shot, so the cooldown is faster after every shot.

 

To avoid this, we must warm the mag. If we have a very heavy mag, with a lot of metal with high specific heat, the liquid has more heat in the metal so cooldown is smaller, but will take more time to warm the mag once we shot.

 

I'm making my own CO2 valves to converts my GHK and pistol gas mags to CO2. At first I thought as BaBaBooey about the valves, that only matters the cross section. But after testing some of my valves I have found that the groove in the side, where the side holes are, is VERY important.

 

I also don't like the valve lock desing, but I have found that is essential if you use heavy bolt carriers and recoil springs.

 

When I was using R-410a, it was very hard to fill the mag. At first, when the pressure in the mag was low, the liquid go into the mag easily. But once the vapor pressure in the mag equals the vapor presure in the can, the hidrostatic pressure of the can could not win the surface tension of the liquid in the small hole of the can adapter, so I can't fill the mag with liquid and only get a few shots. To solve this I put the mags in the fridge before filling them, so the filling operation is easier. With this metod and R-410a I could shot 225 shots with a GHK M4 mags and more than 90 whis a KJW M9 mag with only one fill of gas.

 

About the bb weight: when you use 0.20 or 0.25 in an AEG, you get a faster velocity with 0.2 than 0.25, but the energy is the same. This does not happen with gas guns.  Using heavier bbs in a gas gun get higher muzzle energy than light ones. I have made an Arduino chronograph to study this deeper, but I have blow one of my expensive sensors so I'm wating to make a better hardware.

[Algy]

...I hear you can alter fps output by cutting the floating valve for example? How does that work? How does the strength of the floating valve spring affect power? Does it affect gas efficiency?...

I had a problem with low power output with a gbb pistol not long ago.

NonEx (very astutely) suggested stretching the floating valve, so that more gas would reach the bb before closing the valve: http://www.arniesairsoft.co.uk/forums/index.php?/topic/207993-kjw-co2-magazines-fps-lower-than-green-gas/

 

The stiffer spring tension led to an increase of gas pressure on the bb, but at the time I also perceived an increase in overall gas consumption. However, I'm not sure that gas consumption can be affected by the floating valve spring, as it is the knocker valve that controls the amount of gas, so the gas consumption going up could have been my imagination/weather/gremlins.

[renegadecow]

A lot of things can cause increase/decrease of gas consumption on a negative pressure gas system. By increasing spring tension of the floating valve, you're prolonging dwell time before it closes meaning more gas is pushed out the muzzle before gas is diverted to blow back.

[BaBaBooey]

The next component in most GBB pistols is the rear chassis - depending on the make and model of your pistol, there may not be a separate rear and front. Some Marui pistols (e.g. 1911) only have a single chassis that they refer to as the inner frame. The Marui PX4, P226E2, Five-Seven, etc. does use a separate rear chassis (as do certain WA pistols).

If your pistol does not have a separate chassis, these parts might be installed directly into the frame or inner frame. The typical components here are (this is taken off a Marui P226E2; it's important to note for Marui P226 owners, most of these parts were redesigned on the E2 and cannot be interchanged between the R and E2):

A. Hammer
B. Valve Knocker Spring
C. Valve Knocker
D. Valve Knocker Lock
E. Sear Spring
F. Sear



H is the section of the valve knocker that is struck by the hammer; it also serves as the pivot point which allows the entire knocker to pivot up. Again, this pivoting action is needed so when the knocker is fully extended, you can insert a magazine without it venting. G on the hammer is the section where it strikes the valve knocker.

One important point here: you should NOT replace the hammer with a real gun equivalent even if it appears to be the same. Airsoft hammers are specifically designed to make contact with the knocker and real gun hammers are obviously not (G of the hammer on real guns will be missing).

The photo below shows the rear chassis attached to the slide (looking up), again a Marui P226E2. Notice that there is a guide (I) on the blow back unit of the slide. This is the guide where the vavle knocker lock (D) travels under. This guide ends right about where the opening in the cylinder is (J - pointed out by the punch tool). Also note that the photo shows the pistol at "rest" or at the immediate point when the trigger has been pulled on a cocked pistol: the knocker lock (D) is up and will prevent the knocker, C, from retracting - it can only be fully extended as long as the lock (D) is up. The hammer is also making full contact with the knocker; as long as the hammer is up, the knocker cannot be retracted. With the knocker extended, it is opening the main magazine valve and gas is traveling up into the slide (or will pivot up for an un-chambered/un-loaded gun). Again, on certain WA pistols, this process is reversed (knocker retracted when hammer is up).

On a side note - this is why most Marui pistols cannot be fully de-cocked as it will immediately extend the knocker, opening the main magazine valve (the guide (I) on the slide will put the lock in the up position). It can only be put into a fully cocked or a "half-cocked" position when chambered with a BB.

 

J shows where the guide (I) on the blowback unit ends. When the slide blows back, as soon as the valve knocker lock reaches J, it (D) will get pushed down into the chassis. Once the lock is pushed down, the valve knocker can and will immediately retract into the chassis (it is pushed by the knocker spring - B. The photo below shows the position of the chassis with the slide fully pulled back:



Note that the valve knocker, C, is now fully retracted inside the chassis. At this point, the main valve on the magazine will close, cutting of the gas flow into the cylinder. On WA pistols, the lock functions differently - from my post above, the knocker lock interfaces with a valve lock attached to the magazine that will let the valve close.

What does the chassis look like as the pistol cycles...

[BaBaBooey]

Sorry - let me qualify my de-cocking statement. You CAN fully de-cock a loaded Marui P226E2 or R by removing the magazine. After the magazine is removed, just pull the trigger to let the hammer back up...then re-insert the magazine and you're ready to go. Even though the valve knocker is fully extended, it will NOT open the magazine valve (since it will pivot up).

[BaBaBooey]

Cont'd from above - this is what the rear chassis components look like. What's not shown in any of the photos is the valve knocker lock spring. The knocker lock compresses this spring which forces it to be in the up position. On most Marui guns, this spring is held inside a channel carved into the chassis and difficult to show in photographs.

 

So going over the stages again:

 

Stage 1: A fully charged magazine is inserted into an "un-cocked" gun - again, even though the knocker is fully retracted, it will not open the main magazine valve since the force of pushing the magazine up into the pistol will tilt the valve knocker up.

 

Stage 2: The slide is pulled back to chamber a BB. Moving the slide back will move the hammer down - once fully cocked back, the sear spring will tilt the sear against the hammer and lock it into place (C - on certain models, you might also have a separate part called the disconnector; P226's don't have them...without going into too much details, it helps prevents the gun from going into full-auto). Remember from the post above, once the slide is fully pulled back, the slide will push the knocker lock down (A). Now both the knocker lock and the hammer is fully depressed so the valve knocker can retract into the chassis (B) through the help of the valve knocker spring.

 

At this point, the gun is loaded, cocked, and ready to fire; the chassis components will appear to be set like so:

 

 

Stage 3: The trigger is now pulled and pushes the sear (D) back to the original position, releasing the hammer. The hammer spring will force the hammer back to the original position; as it moves back up, it makes contact with the valve knocker (at E1). As it contacts the knocker, it is pushed out of the chassis (at E2), contacting the main magazine valve, opening it, and sending gas into cylinder to fire the BB. Before the blowback begins, the valve knocker will remain locked in the fully extended position since the slide is at battery which allows the valve knocker lock to move into the up position (F).

 

At this instant, as long as the knocker is fully extended, the magazine will continue venting gas into the cylinder. The chassis components will appear to be set like so:

 

 

After the BB is fired, the cylinder valve inside the slide will close sending gas back towards the slide to cause blow back. The slide blowing back trips the knocker lock, retracts the knocker (thus closing the valve and stopping the gas flow), and re-sets the chassis back to Stage 2 described above. It's now ready to fire the next BB or stay lock back if the last BB was fired.

[BaBaBooey]

On a side note - for majority of the Marui pistols, the valve knocker is not centered with the gun. Looking directly back towards the hammer (as if you're looking down into the barrel), it looks like this (the left hand side of the chassis cover is removed and not shown):

 

 

The knocker is only hitting a fraction (about half) of the magazine main valve surface. If you actually look at the magazine, you'll notice that the channel that the knocker travels against is off centered too. I'm not really sure why Marui pistols are designed this way? My guess is that if it's fully centered, the valve knocker might not tilt up when a charged magazine is inserted into the gun causing it to vent?

[BaBaBooey]

This is a scenario we want to try and avoid. Note that the hammer is down, but the valve knocker lock is still in the up position, preventing the knocker from retracting - the chassis parts should never end up at this setting, but it can happen for a quick second. As a result, the gun will continue to vent gas even though the blowback cycle is over, the hammer fully cocked, and the BB fired.

 

 

What might cause this? Depending on the make and model of your gun, short stroking might do this since your slide is not traveling back fully. From my experience, a poorly assembled metal kit or a loose blowback unit may do this to a Marui P226. Remember that the channel in the blowback unit controls the movement of the knocker lock. If the slide is not correctly made, it will not hold the blowback unit correctly. As a result, the channel that the knocker lock travels under gets slightly misaligned with the knocker lock and throw off the timing of the blowback cycle. A poorly assembled frame will also do the same - the chassis will be out of position resulting in a misaligned knocker lock. On a good P226 metal kit, the rear chassis should fall into the frame - if you find your self putting a lot of pressure on it or removing material off to get it to fit, something is not correct.

 

Especially difficult to assemble are the Guarder P226 kits - the Guarder kit requires you to remove material from the original blowback unit. If too much/not enough material is removed, you end up with blowback unit that is not installed correctly (the cylinder opening will also be misaligned with the magazine gasket, which is an even bigger issue). The end result is a pistol that is unnecessarily venting gas out of the ejection port (it actually looks kinda cool, but you don't want it to happen) and not as efficienct as it could be. Just based on my own experience, the blowback unit comes loose fairly easily on ProWin/PGC P226 kits. Make sure your blowback units are reasonably secured (on the P226, check if the rear sight is loose or not fitting correctly - this is an indication that something is wrong) and centered correctly along the axis of the slide. 

 

I think that's it for the frame? We can look at the slide components and begin to look at things like negative/positive pressure, rocket valves, blowback, etc.