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Best way to prevent jams


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#1 SnowboardeR1298

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Posted 22 May 2013 - 10:07 AM

I am currently running a stock lm4 but I have the evoII hop up en route to be installed. Occasionally I'll get jam where one bb is in the hop up chamber and another one is on the feed ramp. The one on the feed ramp is obviously the one that causes the jam, but I was curious if there was a way to prevent this from happening. It happened to me last weekend during a game and all I can say is its a good thing I wasn't rushing the opfor or I'd have been hit.

#2 thatguyx

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Posted 22 May 2013 - 11:17 AM

Replace your piston o ring with a harbour freight green nitrile ring. Make sure you get really good compression. Also don't feed more than 40 BBS in a usgi mag, 38 in the pmag. Don't accidently try to double load bbs. (One in the hop up and then adding a new mag and loading another bb into the hop up.

#3 SnowboardeR1298

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Posted 22 May 2013 - 03:16 PM

View Postthatguyx, on 22 May 2013 - 11:17 AM, said:

Replace your piston o ring with a harbour freight green nitrile ring. Make sure you get really good compression. Also don't feed more than 40 BBS in a usgi mag, 38 in the pmag. Don't accidently try to double load bbs. (One in the hop up and then adding a new mag and loading another bb into the hop up.

Would it be the 205 piece HNBR O-ring kit? And ok thanks. What if ones in the chamber and I put a new mag in and shoot without putting another round in?

#4 Lost

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Posted 22 May 2013 - 04:33 PM

If a bb is in the chamber and you put a new mag which has 40 bbs, the LM4 will jam. I believe the LM4 needs 3mm clearance in the magazine in order to cycle correctly.

#5 thatguyx

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Posted 22 May 2013 - 04:56 PM

yup the 205 green o-ring kit ~$15.  Sucks you only need one size, but there's like 10 of them.  Maybe you can sell a few to some other lm4 users local to you for a buck to recoup.

as for your other question huh?  If you have a bb in the chamber, don't do anything to load another bb on top of it.  For example: there's still  a bb in the chamber and then you put in a fresh mag and rack the charging handle(which feeds another bb into the already loaded chamber) OR your bolt locked back prematurely and there's still a bb in the chamber and you reload a fresh mag and send the bolt foward(again loading another bb onto the previous).  

You can do a tac-reloads (switch mags when the bolt is in battery (a bb in the chamber) no problem.

#6 SnowboardeR1298

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Posted 22 May 2013 - 05:21 PM

Cool, just ordered them.  And yes, like you said at the last bit of that reply. That's what I'm talking about. Having one round in the chamber with the bolt forward, switch mags, and start pulling the trigger again. That's ok, right?

#7 thatguyx

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Posted 22 May 2013 - 05:39 PM

View PostSnowboardeR1298, on 22 May 2013 - 05:21 PM, said:

Cool, just ordered them.  And yes, like you said at the last bit of that reply. That's what I'm talking about. Having one round in the chamber with the bolt forward, switch mags, and start pulling the trigger again. That's ok, right?

yup, that would be a tac-reload

#8 SnowboardeR1298

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Posted 22 May 2013 - 06:26 PM

View Postthatguyx, on 22 May 2013 - 05:39 PM, said:



yup, that would be a tac-reload

Awesome. Thanks for the reply. And btw, great videos on YouTube man, keep them coming!

#9 BoobieM4H

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Posted 22 May 2013 - 09:15 PM

Stake the outer barrel to the hop up unit..over time the recoil will cause the hop up unit to move in a lateral motion in the outer..and cause jams. Staking the barrel to hop up unit will prevent this movement.  I've done this to countless lm4's..and NONE have came back to me with jamming issues.

( o Y o )



#10 Chuck S

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Posted 23 May 2013 - 02:52 AM

Got a photo of the stake point(s)?

With no extractor (that would be a good trick) it's fairly easy to cause a double feed during a reload if you cycle the bolt carrier.  And it's much harder to clear in the LM4 than the M4.

-- Chuck

#11 BoobieM4H

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Posted 23 May 2013 - 06:11 AM

View PostChuck S, on 23 May 2013 - 02:52 AM, said:

Got a photo of the stake point(s)?

With no extractor (that would be a good trick) it's fairly easy to cause a double feed during a reload if you cycle the bolt carrier.  And it's much harder to clear in the LM4 than the M4.

-- Chuck
Its kind of a stake/crimp ..ill try to do a video of the next lm4 I build ..which will be soon.

( o Y o )



#12 thatguyx

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Posted 23 May 2013 - 06:12 AM

For what its worth I noticed the lateral movement of the hop up and inner barrel too. I think it was the constant toying with the barrel that sightly wore the barrel collar to the brass piece that secures the whole unit. I put a dollop of super glue into the collar to tighten the tolerances and the movement is gone for now.

#13 akiraspeedstar

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Posted 23 May 2013 - 06:26 AM

I've always ran electrical tape on the inner barrel in front of the hopup/inner barrel clamp (gold piece) to prevent that lateral movement. Which is probably why I've never experienced a double feed other than from user error.

A few wraps of electrical tape hasn't ever failed me yet.

#14 BoobieM4H

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Posted 23 May 2013 - 07:19 AM

Well no need for my video here then..since etape "fixes" things. If y'all wanna know just pm me..like I said..and y'all know..I work on countless LM4's..not just my personal LM4

( o Y o )



#15 akiraspeedstar

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Posted 23 May 2013 - 07:34 AM

Not saying your fix isn't a great idea, especially since it'll permanently fix it. I also didn't state that this was a fix all for everyone, just stated what has worked for me.

Edited by akiraspeedstar, 23 May 2013 - 07:37 AM.


#16 -wigs-

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Posted 23 May 2013 - 07:13 PM

As stupid as this may sound, do you have any reciever wobble?
Mine had none the first few weeks then it creeped it. It got to a point where occasionally if I fired the gun not perfectly up and down it would rock and jam. Fixed by a hood acuwedge. If there's wobble try stuffing a foam earplug under the rear takedown post and see I'f it helps at all.
It fixed my jams with proof enough to say onece the plug is flattened for a while i get some of the slight wobble back and an occasional jam.

Edited by -wigs-, 23 May 2013 - 07:18 PM.


#17 The Nutty Professor

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Posted 23 May 2013 - 07:42 PM

Boobie post the video. I don't do tape fixes. Down here the heat will turn it into a friggin mess so....NAH JACK!

#18 SnowboardeR1298

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Posted 24 May 2013 - 09:12 AM

View Post-wigs-, on 23 May 2013 - 07:13 PM, said:

As stupid as this may sound, do you have any reciever wobble?
Mine had none the first few weeks then it creeped it. It got to a point where occasionally if I fired the gun not perfectly up and down it would rock and jam. Fixed by a hood acuwedge. If there's wobble try stuffing a foam earplug under the rear takedown post and see I'f it helps at all.
It fixed my jams with proof enough to say onece the plug is flattened for a while i get some of the slight wobble back and an occasional jam.

Actually, it does. Not much but enough to bother me. Could you elaborate on the fix a little more?

#19 thatguyx

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Posted 24 May 2013 - 03:10 PM

About the upper wobble, I think its mostly due to the paint wearing off around the connection points of the receivers. That means you KWA, use better paint or change your dimensions to fit better and not paint those areas. Why did you not take this into account during measurements or painting?


But for those of us who already have their lm4s, Ive had success getting rid of most of the wobble by gluing shims to the front joints of the lower and rear points of the upper. They're larger than AEG shims,the receiver pins actually go through the middles. but the method still stands. What little wobble remains was fixed with some tiny strips of electrical tape, until I can find the right thickness of shims.

#20 -wigs-

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Posted 25 May 2013 - 11:18 PM

I'll take pics of what I did to fix the wobble. In all honesty the 3-4 jams I had I just did a straight manual of arms. Ripped the mag out and rack, rack, rack till it went to full battery and I saw no bbs and boom back in the game. Mind you every jam I had was under pressure and mid fight, I wouldn't recommend doing it.

Edited by -wigs-, 25 May 2013 - 11:18 PM.





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