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Poor Performance of my lm4

Lm4 magpul poor performance

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#1 KeithHK

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Posted 23 February 2014 - 01:44 AM

Hi everyone. I am from Hong Kong and English isn't my mother language so if there is any mistake in my language, I feel sorry for that and plz kindly let me know.

Well, back to the topic, I have recently bought the lm4 pts magpul. I was so excited to do some damage with it so I filled in the gas and had a few shots. I went on to the full auto at first. It was fine at the first few shots but then its bolt slowed down and psssssshhhhhhh after about 20 shots. All gas was gone in the mag and the valve can be easily pressed down. It isn't very cold in Hong Kong even in winter time. The temperature was about 17 degree Celsius when I shot the lm4 (sorry that nobody here in hk use degree Fahrenheit) I was really depressed by the poor performance. I had a kwa mp7 also and it is still working fine. Is there anything wrong with my lm4? What can I do to improve its performance?

Thx in advanced.

#2 phillyc220

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Posted 23 February 2014 - 03:17 AM

Welcome to the forums.

My first question is if your are using green gas or propane. What could be the issue is that if your using green gas, the bottle may be almost empty. Using a fresh new can would do the trick. Try that first and see if that fixes your issue.

#3 Chuck S

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Posted 23 February 2014 - 04:33 AM

Sounds like you're running out of gas.

You can't overfill a gas blowback magazine.  I fill my LM4 magazines with Green Gas for 45 seconds.  Fill valve up, can nozzle down 'cuz they fill with liquid, not gas.

When the magazine nears empty the gun slows down and at the end often goes pssssssttttttt (note the different spelling :) ) when there's not enough recoil to remove the hammer from the valve on the rear edge of the magazine.

-- Chuck

Edited by Chuck S, 23 February 2014 - 04:33 AM.


#4 KeithHK

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Posted 23 February 2014 - 07:47 AM

Thanks for answering. My bottle of green gas is a new one but the problem stills exists. Besides I only fill my mags for around 10 seconds. Is there any problem with my rifle? Do you guys face the same problem?

Edited by KeithHK, 23 February 2014 - 07:48 AM.


#5 Rockhound117

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Posted 23 February 2014 - 10:23 AM

Ten seconds is certainly not enough time filling the magazine. I would recommend you do as Chuck S and fill the mag for 45 seconds. Also, though I know your gun is new, I would break it down and make sure the nozzle o-ring looks okay and is properly oiled along with the rest of the bolt carrier group. And just to be sure, I would stick the mag in my back pocket and let it warm up. 17°c (~60°f) isn't that warm in my opinion. If, after all of that, it still malfunctions, then we can probably rule out user error and assume there is something wrong with the rifle.

#6 Downs

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Posted 23 February 2014 - 10:28 AM

10 seconds for a gas fill?  Not nearly long enough.  The gas resiviour on this magazine is HUGE. I think that when you fill for 30 to 45 seconds you will get much better performance.  I can get around 2 full magzines out of one gas charge.

#7 Jakeedaman21

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Posted 23 February 2014 - 11:15 AM

Once the above comments are verified, I think the next step would be to check/oil the o-ring seals in the magazines. If a simple oiling doesn't work it may require something more intrusive like the blu-gasket maker mod to the magazine.

#8 General Pickle

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Posted 23 February 2014 - 02:30 PM

17°C isn't optimal for the LM4 unfortunately, especially on fully automatic. In my experience, anything below 20°C is going to show a decrease in 'normal' performance, though semi-auto should work fairly well.

Another thing which is fairly common is the PMags having leaks. I've found that just about every one of them has a poor seal at the base of the magazine, causing gas to slowly leak out from the bottom. This can be fixed with a gasket maker, as mentioned above, or replacing the rubber seal entirely. In my experience even the replacement rubber seals are not the right size, so gasket maker is the best option.

I also had one of my mags leak from the inner post which is held in place by two screws in the middle of the magazine. I simply flipped the o-rings around and that solved the problems, but maybe you could swap the o-rings entirely if that doesn't work.

Another possibility is the fill valve leaking or the release valve leaking. I tried removing a fill valve, lubing it heavily, then replacing it very tightly and found the problem to be fixed. Same procedure with the release valve, which I found to have some tendency to stick open sometimes.

As was previously mentioned as well, these mags hold a LOT of gas. You'll want to continue charging the magazine until you can't hear anymore gas flowing, or perhaps just counting to 40 or so will do the trick. I use propane, so perhaps my fill times are a bit shorter than those who use green gas.

Good luck, hopefully this helps you solve the problem!

#9 KeithHK

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Posted 23 February 2014 - 04:49 PM

Thanks a lot guys. I have shot it in semi-auto mode also. Nevertheless, after about 30 shot, it went psssssssttttt. I will try it again later and will fill the mag for 30 seconds approximately. Hope everything is doing well. I will soon come back with u guys and let u know how my rifle is doing. Really thx a lot.

Edited by KeithHK, 23 February 2014 - 04:49 PM.


#10 KeithHK

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Posted 23 February 2014 - 11:19 PM

I have just tried my lm4 again after lubing it. I follow your advice and the gun did a better job. At least it went for a few more shots before it went psssssstttt.

Edited by KeithHK, 23 February 2014 - 11:19 PM.


#11 Jatodude

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Posted 26 February 2014 - 03:40 PM

It seems like the plug at the base of the piston is getting stuck. If you're shooting in full automatic, and the rate of fire slows down, then stops and makes a "psssssssstttt" noise, the plug is probably getting frozen inside the piston. This happened to my rifle. I'm not sure about the warranty since you're not from America, but there is a way to fix it.

Here is a tutorial to fix the problem:

#12 KeithHK

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Posted 27 February 2014 - 02:12 AM

Thx dude. May be I need to break down my rifle and modify it. Really thx and I hope the technique is useful.

Edited by KeithHK, 27 February 2014 - 02:13 AM.






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