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Need Some Help Diagnosing A Feeding Issue

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#1 Jatodude



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Posted 30 September 2013 - 08:35 AM

Some back ground: I've got an LM4 that's a year and a half old, that's always had something problematic with it. For the better part of a year I ran it on semi only because it shot poorly on full auto. BB's dropped and it spewed gas every now and then. I replaced the o-ring which helped a little. Then found the bucking had swelled massively. After replacing the o-ring and bucking, it shot fairly well. Still dropping though. Then the spring in my bolt snapped, which I fixed by just making a new loop out of the old spring. Started shooting on auto again to test, still dropping. So I start watching the bolt and testing it when I realize that the piston is getting stuck in the bolt when it freezes up. Made a post, then Boobie made that video to fix the problem. I did the fix, and it worked extremely well. But the mags still blew gas and dropped a little on auto. So I tried something interesting.
Looking at Boobies fix for misfeeding, I took some paper towel and wrapped it around the barrel on both sides of the barrel stabilizer, and presto. After a few shots, everything worked well together and absolutely NO shots were dropping, no gas spewing. Every mag worked like a charm.
So to test my theory, I take the paper towel out and try it again. Testing the newest mag I had with the new round feed lips, it worked perfect. So I try the other older type mags, and feeding issues like I'd never seen before. BB's went everywhere, they consistently flew out the ejection port on full auto every other BB. It was extremely strange. So I tried one of the misfeeding mags again, only this time I pulled down on the mag while firing, and it shot like a dream.

Is the issue related to the mag bouncing around in the magwell when firing? Is the inner barrel shaking around?

It seems to me that the barrel isn't stabilized well, and needs the misfeeding fix that Boobie shows on his YouTube channel. But I'm perplexed as to why one of my mags feeds perfectly fine. Stuffing paper towel on the brass stabilizer works fine as a temporary fix, but I'd like to know what's wrong with the mags.

Can anyone offer some of their expertise?

#2 netpoc



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Posted 02 October 2013 - 03:58 PM

Did you do my fix that prevents the barrel from shifting back and forth? Cut a shallow groove with a dremel just behind the brass inner barrel stabilizer and use a c-clip (not an o-ring, as mine failed...) to prevent the inner barrel stabilizer from sliding back and forth on the barrel. Next, is to check that your piston is moving freely back and forth in the bolt. Not too loose and not too tight. Probably most important in the whole thing is to make sure that your gun is not over lubed anywhere. The entire gun should be relatively dry aside from a very light oiling of the piston o-ring.

#3 niko_gpsy


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Posted 03 October 2013 - 10:25 AM

Can you take a look at both the old and new mags side by side?  Check to see if the opening for the mag catch is different somehow even by a little (such as position, length and wear on opening).  Also check to see if your mag catch is loose.  May need to tighten down the screw a bit if it is.

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