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Broken BBs


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#1 kwaispro727

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Posted 21 January 2014 - 11:19 AM

This whole issue may just be an effect of the cold weather on my gun, but I'm not entirely sure so I thought I would post.  Every time I put a mag in and charge it, the first 3 shots are guaranteed to be fine.  After that, it's a crap shoot.  What happens is either one of two things, the gun will perform flawlessly, or this weird type of jam i've never experienced in a GBB happens.  I only run KWA BBs at the moment.

I noticed that occasionally, the bolt will not return completely.  The carrier sits about 1 centimeter back from it's regular closed position.  When this happens, if I lock the bolt back and eject the mag, one BB will fall out.  After that, if I open the gun, another cracked BB will be sitting in front of the hammer.  Attempting to fire the gun with the bolt not completely returned results in the release valve getting stuck and losing all the gas in the mag.

I can't tell if it's the magazine, the BBs, the bolt lubrication, or what.  I lubricated the bolt before it happened again today so I think it's safe to rule that out.  I shot it out the back door of my house.  It's about 65 degrees inside with around 25ish degree air flowing in the door.

Nothing like this has ever happened with my m9, or my mp7 (sold), or my atp auto (sold).  I've never seen it in a G&P gbbr either.  Ideas?

#2 General Pickle

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Posted 21 January 2014 - 11:27 AM

Holy hell, do you mean that BB's actually got into the trigger group? If that's the case then I'm not sure what's going on, but from the sounds of that I think you may be having the classic LM4 'double feed' issue.



Credit to Boobie for the video, I just share it with whoever needs the information.

#3 netpoc

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Posted 21 January 2014 - 12:34 PM

Make sure you clean all of the broken bb pieces out of the "chamber" area (the area that the "gear" end of the bolt goes into), as well as the trigger group areas, or you will continue to have jamming issues. Take note of the video above: boobie was kind enough to make a video of an idea I had to limit movement of the inner barrel.

#4 kwaispro727

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Posted 21 January 2014 - 01:54 PM

The BBs don't get into the trigger group.  It just sits there, with a crack in it.  It's still in once piece though.  Like the bolt smacked it and it just cracked.  
Here is what the jammed bolt looks like:
Posted Image

Here is what it should look like for comparison:
Posted Image

And this is where a BB ends up:
Posted Image

#5 General Pickle

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Posted 21 January 2014 - 02:33 PM

Wow. :wtf2:

#6 kwaispro727

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Posted 21 January 2014 - 03:24 PM

I honestly cannot figure out what is going on, or how it jams.  

Let's assume it does double feed, how the f**k does a BB make it's way to that spot in front of the hammer?

If it's not double feeding... how is the second BB getting out of the mag... and why is the bolt carrier not going all the way forward?

I'm completely stumped.

#7 SR105

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Posted 21 January 2014 - 03:27 PM

When you have a chance can you take a good picture of your bolt face please?

#8 kwaispro727

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Posted 21 January 2014 - 05:43 PM

Looks fine to me.Posted Image

#9 netpoc

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Posted 21 January 2014 - 06:07 PM

Make sure the feed lip on the magazine(s) are not cracked or broken. I had a similar issue from a cracked feed lip, except the second bb was ejected out the ejection port.

#10 kwaispro727

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Posted 21 January 2014 - 06:28 PM

Feed lip is all good.

#11 PonZee

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Posted 22 January 2014 - 04:24 PM

kwaispro727, I would highly, HIGHLY recommend you perform the fix that General Pickle posted earlier in this post. I was having the exact same issue as you and ended up tossing my LM4 to the side when I was out for a day of airsoft. I would fire a couple of rounds and then a BB would get caught where the hop-up area was and ended up stuffing itself in there, subsequently causing it to be crushed and leave fragments of sh*t everywhere. I have since unloaded multiple mags in full auto and such with no issues whatsoever. It is indeed the "double feed" issue. I even had one BB travel back into where the hammer was and under the selector switch.

The fix posted literally takes 5 minutes if you have a dremel in your possession.

Edited by PonZee, 22 January 2014 - 04:25 PM.


#12 kwaispro727

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Posted 22 January 2014 - 06:34 PM

Hmm ok I'll try it.  Seems a bit ridiculous that this problem went unnoticed in testing before the gun was released what, last year?  And unfixed in newer models for that matter. Back to work with the dremel lol

I still want to know exactly how it's double feeding though.  Maybe I'll set up a camera and re-create it then slow it down and have a look, before I fix it.  I don't really understand how swollen buckings and misplaced hop-ups/barrel parts cause a double feed.  How do any of those things effect the chambering of a single BB? It's not like it's bouncing the bolt back a 2nd time and allowing another one to be fed in... or does it? o_O

#13 PonZee

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Posted 23 January 2014 - 10:25 AM

View Postkwaispro727, on 22 January 2014 - 06:34 PM, said:

Hmm ok I'll try it.  Seems a bit ridiculous that this problem went unnoticed in testing before the gun was released what, last year?  And unfixed in newer models for that matter. Back to work with the dremel lol

I still want to know exactly how it's double feeding though.  Maybe I'll set up a camera and re-create it then slow it down and have a look, before I fix it.  I don't really understand how swollen buckings and misplaced hop-ups/barrel parts cause a double feed.  How do any of those things effect the chambering of a single BB? It's not like it's bouncing the bolt back a 2nd time and allowing another one to be fed in... or does it? o_O

Yeah, it's crazy. If you watch the video you'll hear that apparently what happens with the lm4 is that when you fire your weapon, the bolt eventually pushes the hop up forward against the inner barrel so the following rounds don't feed properly or something. It has something to do with the entire mechanism sliding around know the inner barrel.

It is odd that this issue remains even after new batches exit production and stuff.

#14 kwaispro727

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Posted 23 January 2014 - 03:51 PM

So you're saying the misplaced hop-up assembly and bolt allow two BBs to feed?  Is there really THAT much movement?  I gotta see this for myself.

#15 Theshank

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Posted 26 January 2014 - 02:07 PM

I did the mod in the video and it solved my problem of double feed, jam up hell. ( I was about ready to give up on this thing). Lol. It shoots great now.
Have fun figuring out which hop up to tinker with for your fixed position hop up. Once you get it to shoot leave it alone.




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