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How "sticky" Is The Piston Supposed To Be?


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#1 airsoftsniperm4

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Posted 30 May 2012 - 12:44 AM

Got my lm4 last week, been fiddling with it, impatiently waiting for my next order green gas to get here already. Something I've noticed is the piston is sticking forward quite a bit after the bolt is back pretty far. Is this normal? I've also seen that sometimes the piston doesn't lock back all the way after the last shot is fired, it'll be sticking out by about 2 1/2"-3" past the bolt when it's locked back. Is that normal for the first 500 shots or so?

Here's a pic of about how far I can pull the bolt back before the piston will shoot back into the bolt all of the way. I'll try to nab a picture as soon as I can if the piston doesn't return all the way after the last shot is fired.
Attached File  ImageUploadedByTapatalk1338367398.337526.jpg   235.54K   38 downloads


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#2 Nitemare

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Posted 30 May 2012 - 05:45 AM

That is normal to ensure a good seal when expelling gas to propel the BBs. As for the piston not locking back all the way, I have this problem as well as have other people. It is supposed to be a break-in fixable issue (as in, after a thousand or two rounds it'll be fine).

#3 Guest_Allizard_*

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Posted 30 May 2012 - 08:48 AM

Did you use any spray type silicon around the nozzle and hop-up area?

#4 airsoftsniperm4

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Posted 30 May 2012 - 09:20 AM

View PostNitemare, on 30 May 2012 - 05:45 AM, said:

That is normal to ensure a good seal when expelling gas to propel the BBs. As for the piston not locking back all the way, I have this problem as well as have other people. It is supposed to be a break-in fixable issue (as in, after a thousand or two rounds it'll be fine).

Ok, that's what I figured. Just wanted to make sure though.

View PostAllizard, on 30 May 2012 - 08:48 AM, said:

Did you use any spray type silicon around the nozzle and hop-up area?

I did not, but I ran about three or four mags through with putting a drop of silicon on the GG bottle's tip.


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#5 Outlaw1995

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Posted 30 May 2012 - 12:39 PM

I've experienced this as well, and I think Nitemare's explanation of why it is caused is valid. Unless it prevents the bolt from actually cycling, I do not see any issue with it.

#6 airsoftsniperm4

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Posted 30 May 2012 - 01:35 PM

View PostOutlaw1995, on 30 May 2012 - 12:39 PM, said:

I've experienced this as well, and I think Nitemare's explanation of why it is caused is valid. Unless it prevents the bolt from actually cycling, I do not see any issue with it.
It doesn't seem to be harming it at all.
Reason I'm asking is I'm having issues firing on full auto. It'll shoot and cycle fine, everything sounds normal, but a few bb's will shoot fine, normal distance, then about 5-10 will fall about 15 feet from the barrel. Any ways to diagnose this?
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Edited by airsoftsniperm4, 30 May 2012 - 01:36 PM.


#7 Guest_Allizard_*

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Posted 30 May 2012 - 05:47 PM

When the cylinder have a delay retracting back into the bolt will affect the timing of loading the next BB into the hop-chamber.  This may cause the BBs to roll out.  Try cleaning the hop-up opening and the hop-up bucking with a Q-tip soak with soapy water.  Let it dry and try shooting it again.

#8 BoobieM4H

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Posted 30 May 2012 - 10:54 PM

i had this same problem too..until i swapped out the hop up rubber with  a ksc m4 bucking. all my shots now are consistant ..even on full auto. and yes it is normal for the nozzle to "stick". the seal between nozzle and chamber is good.stock oring didnt make good compression on my LM4.. so i changed the oring on the piston head to a slightly bigger one and compression is better.

#9 airsoftsniperm4

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Posted 03 June 2012 - 04:03 PM

Got my bottle of green gas yesterday, and I've only been getting around 40 shots out of each mag with the last 8-10 being very weak before the mag needs to be refilled on gas. I tried the green gas through a mag on my M17, then a mag of propane, and the propane would get almost three times the rounds through the gun before needing to be refilled. It seems like its taking around 45 seconds to fill the M17's mag, and I still can't tell if its full or not. Is this normal for green gas or did I just get a bad bottle/adaptor?

Anyways, I'm still having the full auto trouble, about to try what Allizard mentioned and I'll report back.

Can I fire a mag of propane through the rifle without it voiding the warranty just to make sure that its the green gas and not the gun or magazine that is making the lack of shots fired happening? When filling the lm4's mag, I have to fill it long enough to basically make my arm cramp up before it'll fire through 30+ rounds.

#10 greatwatermelon

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Posted 03 June 2012 - 05:35 PM

Propane will void your warranty.

How empty is your Green Gas can? You may want to try a new green gas can. It sounds like your GG can has been used quite a bit.

#11 BoobieM4H

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Posted 03 June 2012 - 08:05 PM

What brand green gas are you using? If its the type that has the screw on nozzle then itsproobably the nozzle..and that green gas sucks imo..the brand of that is "power green gas". Try using king arms gg. Its the best out there right now in the states  that I can find. I'm also using a brand called "puff dino" its 1000ml..tall can.

#12 airsoftsniperm4

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Posted 03 June 2012 - 09:05 PM

View Postgreatwatermelon, on 03 June 2012 - 05:35 PM, said:

Propane will void your warranty.

How empty is your Green Gas can? You may want to try a new green gas can. It sounds like your GG can has been used quite a bit.

It is a brand new can. Just spend $17 on this can and I can't even use it...and I have tons of propane laying around.

View PostBoobieM4H, on 03 June 2012 - 08:05 PM, said:

What brand green gas are you using? If its the type that has the screw on nozzle then itsproobably the nozzle..and that green gas sucks imo..the brand of that is "power green gas". Try using king arms gg. Its the best out there right now in the states  that I can find. I'm also using a brand called "puff dino" its 1000ml..tall can.

It is the screw on nozzle type sadly. I didn't know that it was screw on otherwise I wouldn't have gotten it.


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#13 BoobieM4H

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Posted 03 June 2012 - 10:09 PM

yea..thats your problem then..you can bore out the hole to a larger diameter on the screw on tip..use a very small drill bit slightly larger and tap into nozzle from the bottom.the part that screws into can..tap into it halfway..dont go all the way to the tip..thats if you want to salvage whats left of that can.

and try to stay away from the propane..ive tried that before and ive only experienced the worse with it..broken nozzles, dried up piston head orings, mag leaks.

#14 greatwatermelon

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Posted 03 June 2012 - 11:41 PM

Yeah that Power Green Gas can is infamous.

Propane works, but doesn't mean it works well. This is not just for KWA's, just GBB's in general. I've seen a store dedicated to GBB try using propane and suddenly make a switch to GG only. It doesn't take much to connect it together.

#15 gcw360

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Posted 04 June 2012 - 08:30 AM

View PostBoobieM4H, on 03 June 2012 - 10:09 PM, said:

yea..thats your problem then..you can bore out the hole to a larger diameter on the screw on tip..use a very small drill bit slightly larger and tap into nozzle from the bottom.the part that screws into can..tap into it halfway..dont go all the way to the tip..thats if you want to salvage whats left of that can.

and try to stay away from the propane..ive tried that before and ive only experienced the worse with it..broken nozzles, dried up piston head orings, mag leaks.
BoobieMH4 is spot on here.  Power Green used to come with an integrated nozzle and it worked fine.  As soon as the screw on nozzle came out there were nothing but issues.  It's not only with KWA GBB's by the way.  I tried filling a brand new TM PX4Storm and could only empty half a mag using a new can of Power Green.  KA brand is good as is KWA's brand.

If you can get the 1000ml cans (various brands) I would try them.  Reports are that they seem to work better than the shorter cans.

#16 airsoftsniperm4

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Posted 04 June 2012 - 10:38 AM

Ahh I see. At first I could only empty about half of the mag per fill. Another thing is that it leaks gas while filling unless the angle is perfect and there is a lot of pressure applied. It just seems like there isn't enough pressure in the can to fill the mag how it should be. I'll try drilling the hole out a little and see how that helps.


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#17 airsoftsniperm4

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Posted 12 June 2012 - 04:30 PM

I tried what Allizard said, and I'm still having issues on full auto. If I do a burst of two or three rounds, it'll shoot fine, but as soon as I try 5 or more, bb's start falling short. I also noticed that if I hold it for maybe 8-10 cycles, shots on semi auto following that burst will fall short as well. This is with KA green gas, I'm getting about 4 mags of 35 rounds through each fill.


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#18 Jatodude

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Posted 12 June 2012 - 04:36 PM

View Postairsoftsniperm4, on 12 June 2012 - 04:30 PM, said:

I tried what Allizard said, and I'm still having issues on full auto. If I do a burst of two or three rounds, it'll shoot fine, but as soon as I try 5 or more, bb's start falling short. I also noticed that if I hold it for maybe 8-10 cycles, shots on semi auto following that burst will fall short as well. This is with KA green gas, I'm getting about 4 mags of 35 rounds through each fill.


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This problem is arising from your piston O-Ring. It's freezing up and you're loosing compression.  Try putting some lube on it.  I'm having the same problem.  After lubing it quite generously, it should work pretty decent for a short period.  Mine went through about half a magazine before loosing compression again.  I'm going to try getting a different, slightly larger O-Ring like BoobieMH4 suggests.




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