WE M4 GBB leak?

[CptSchlink]

Ok so I need some help. Hopefully you guys with your knowledge will either know what to do or be able to point me in the right direction. My WE M4A1 GBBR Open bolt is leaking somewhere in the receiver. You can see condensation coming out of the sides of the gun. After consecutive firing (or Full auto firing for 3 seconds or more) you can hear the gun empty out the entire mag of its gas. It makes that "PSSSSHHHHhhhhhhhhhhhh" sound. Thats all the gas leaving the mag at one time after pulling the trigger to quickly.

So when I play I find myself having a very slow trigger pull to avoid losing all the air out of the magazine.

Any suggestions or ideas?

[coach]

When is the last time you broke it down to clean and lube?

[CptSchlink]

After every use. Its been like that since I got it.

[CptSchlink]

Im knew to the hobby. So I hope its not a manufacturers defect. Because I bought it back in January...

[CptSchlink]

I did not know what to look for, or what it should have sounded like, or if that was normal or not..

[Drake]

"Leaks" would occur in the mag, no gas is stored in the receiver.

What you're describing sounds like mags venting due to cool down. To understand cool down you have to understand what happens when a gas gun shoots: similar to a real gun's firing pin, a plunger strikes the main valve on the back of the mag; this opens the valve and allows gas to flow out where its directed into the gun's blow back unit (in the bolt carrier in this case); gas expands inside the blowback unit with some of it flowing forward to propel the BB and some of it pushing towards the rear of the BBU where the piston head is located; as the bolt begins to cycle pressure is taken off the plunger and the valve in the mag closes (due to the gas pressure inside the mag); the bolt carrier cycles, the gun resets.

That's the mechanical part. Inside the mag, you have some proportion of liquid propane and gaseous propane. It remains liquid under sufficient pressure but as pressure drops it will naturally try to transform to gaseous state; this occurs every time the valve is opened. Just like water evaporation, going from a liquid to gaseous state requires energy -- namely heat. This is called an endothermic process. The heat is taken from whatever source is available: ambient heat, but since the gas is enclosed in the metal magazine, heat is taken from the magazine (kind of like a reversed heat sink). When you shoot full auto etc, the mag cools down/outright gets cold. You've probably noticed this. And the mags will have to rely on heat in the ambient air outside the mag to warm up again.

Now the important part (hang in there, we're almost to the punchline): warmer gas has higher pressure, colder gas has lower pressure (relative to its warmer state). If there's a lot of pressure you get more work energy with less gas, which means you're not using as much as per shot to make the gun cycle (and its usually firing at a higher FPS); if the gas is cold, FPS drops and you need more gas to cycle the gun.

Now if the mag is too cold the propane can't draw enough heat, which means you're using more gas, which means you're cooling things off even more (because more propane is trying to convert to gaseous form) and you eventually hit a point where there's so little pressure in the mag (which doesnt mean the mag is empty, there can be a lot of gas left -- it just doesn't have enough heat) the valve can't even push itself closed against the plunger. The result is the same if you kept the valve depressed with your finger, except at a lower pressure.

The gas is venting into your gun and out wherever it can (which is what you're witnessing). Gas systems aren't that great for sustained full auto fire (unless you're caring a huge external gas rig).

There's a few things you can do to help this: obviously ambient temperature is going to have a direct bearing on this, it should be less prevalent on a hot summer day and as the temperature near 5C gas guns become increasingly unusable (with propane anyway);

You probably have an NPAS installed (if you don't, get one, its like $15 and 15 mins of your time to install) so you might want to dial it down. Yes, you'll have lower FPS, but the gun will be more reliable. And honestly higher FPS doesn't mean that much: a good inner barrel, good hopup and heavier BBs will do way more to increase range/accuracy than an extra 25-30 fps. Lower FPS == less gas being used == less cool down;

You can also install a heavier buffer. I personally liked the 69g TSC one but it's hard to find now. But there are others (the buffers advertised as being for WA/G&P fit fine btw). The heavier buffer will slow things down a bit, specially in full auto. Not a hugely noticeable difference, but again every bit helps;

Make sure the piston head in the BBU is well lubed. Wasted gas (i.e., gas leaking out of bad seals) count towards cool down even if it isn't doing any work.

If you're doing a lot of full auto, or playing in colder temps, you might also want to try and use MAPP/Pro gas instead of propane. That's the welding gas in the yellow bottles instead of blue. Lol wut? Yeah, players in Europe use it and refer to it as "winter gas" and while the pressure isn't that much higher than propane under most circumstances (I wouldn't use it on a super hot summer day where your mags are sitting in the sun etc -- see the thread where someone ruptured gas mags from overpressure) it isn't as affected by the cold and much less subject to cool down (even in full auto). Be warned it makes propane smell like air freshener however.

You can also try the WE CO2 mags, might also help a bit. But I dont know under which conditions this happened.

[CptSchlink]

Fantastic Post THANK YOU! Some good suggestions there. I will definitely try to work on some of those things. I have 7 magazines. And if your refering to the person that ruptured two mags that was me, and that was with Propane. So I had 7, now Im down to 5, and they all have the same problem. So if it is a magazine issue as you say, then is it possible that all 5 are doing the same thing??? How do you oil the mags properly to keep them in good shape? Is it just a matter of taking out the valves and oiling the O rings? I have been playing in good temperatures, where it has been warm but not to hot. Around 25 degrees Celsius. I thought that was supposed to be the perfect temp? Maybe its all the valves I need to oil up. I have a RA Tech aluminum nozzle, that has a NPAS kit installed already in it. That did make a small difference when I installed it.
Thanks again for your post. Do you mind answering the few questions??

Originally Posted by Drake

"Leaks" would occur in the mag, no gas is stored in the receiver.

What you're describing sounds like mags venting due to cool down. To understand cool down you have to understand what happens when a gas gun shoots: similar to a real gun's firing pin, a plunger strikes the main valve on the back of the mag; this opens the valve and allows gas to flow out where its directed into the gun's blow back unit (in the bolt carrier in this case); gas expands inside the blowback unit with some of it flowing forward to propel the BB and some of it pushing towards the rear of the BBU where the piston head is located; as the bolt begins to cycle pressure is taken off the plunger and the valve in the mag closes (due to the gas pressure inside the mag); the bolt carrier cycles, the gun resets.

That's the mechanical part. Inside the mag, you have some proportion of liquid propane and gaseous propane. It remains liquid under sufficient pressure but as pressure drops it will naturally try to transform to gaseous state; this occurs every time the valve is opened. Just like water evaporation, going from a liquid to gaseous state requires energy -- namely heat. This is called an endothermic process. The heat is taken from whatever source is available: ambient heat, but since the gas is enclosed in the metal magazine, heat is taken from the magazine (kind of like a reversed heat sink). When you shoot full auto etc, the mag cools down/outright gets cold. You've probably noticed this. And the mags will have to rely on heat in the ambient air outside the mag to warm up again.

Now the important part (hang in there, we're almost to the punchline): warmer gas has higher pressure, colder gas has lower pressure (relative to its warmer state). If there's a lot of pressure you get more work energy with less gas, which means you're not using as much as per shot to make the gun cycle (and its usually firing at a higher FPS); if the gas is cold, FPS drops and you need more gas to cycle the gun.

Now if the mag is too cold the propane can't draw enough heat, which means you're using more gas, which means you're cooling things off even more (because more propane is trying to convert to gaseous form) and you eventually hit a point where there's so little pressure in the mag (which doesnt mean the mag is empty, there can be a lot of gas left -- it just doesn't have enough heat) the valve can't even push itself closed against the plunger. The result is the same if you kept the valve depressed with your finger, except at a lower pressure.

The gas is venting into your gun and out wherever it can (which is what you're witnessing). Gas systems aren't that great for sustained full auto fire (unless you're caring a huge external gas rig).

There's a few things you can do to help this: obviously ambient temperature is going to have a direct bearing on this, it should be less prevalent on a hot summer day and as the temperature near 5C gas guns become increasingly unusable (with propane anyway);

You probably have an NPAS installed (if you don't, get one, its like $15 and 15 mins of your time to install) so you might want to dial it down. Yes, you'll have lower FPS, but the gun will be more reliable. And honestly higher FPS doesn't mean that much: a good inner barrel, good hopup and heavier BBs will do way more to increase range/accuracy than an extra 25-30 fps. Lower FPS == less gas being used == less cool down;

You can also install a heavier buffer. I personally liked the 69g TSC one but it's hard to find now. But there are others (the buffers advertised as being for WA/G&P fit fine btw). The heavier buffer will slow things down a bit, specially in full auto. Not a hugely noticeable difference, but again every bit helps;

Make sure the piston head in the BBU is well lubed. Wasted gas (i.e., gas leaking out of bad seals) count towards cool down even if it isn't doing any work.

If you're doing a lot of full auto, or playing in colder temps, you might also want to try and use MAPP/Pro gas instead of propane. That's the welding gas in the yellow bottles instead of blue. Lol wut? Yeah, players in Europe use it and refer to it as "winter gas" and while the pressure isn't that much higher than propane under most circumstances (I wouldn't use it on a super hot summer day where your mags are sitting in the sun etc -- see the thread where someone ruptured gas mags from overpressure) it isn't as affected by the cold and much less subject to cool down (even in full auto). Be warned it makes propane smell like air freshener however.

You can also try the WE CO2 mags, might also help a bit. But I dont know under which conditions this happened.