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Thread: Help - Weird New Double Feed LMT

  1. #21
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    Silly question but I always check the simple things first- did you strip it down and clean it and then shoot it again? Looks like there is grease or oil/gunk buildup on the BCG and combined with the really cold weather may be affecting bolt velocity.
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  2. #22
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    Quote Originally Posted by LimeSpoon View Post
    Quick question, have you checked extractor spring tension?

    I admittedly don't know myself exactly how this sort of malfunction would happen. But if I were to try to play detective, I'd say:

    1. The rifle previously ran fine with no issues, so this is probably because of some change to the status quo.

    2. It appears this malfunction has only happened when it's cold.

    3. Numerous high quality magazines have been tried so clearly that is not the problem.

    4. Two different, quality buffer springs and 3 different buffer weights have been tried so that is likely not the problem.

    5. The buffer tube is high quality and has not given you issues before. Possible, yes, probable, I don't really think so, or at least it wouldn't be the primary contributor.

    This suggests to me that the malfunction might be the result of wear, temperature-induced sluggishness, or both.

    Now, if I were to try to think of a plausible series of events...

    Enhanced bolts sometimes seem to have weak extractor springs from the factory, for whatever reason. If this were the case then they might have largely worn out after 3000 rounds.

    In normal temperatures this might not have been evident, but perhaps the cold environment is causing an increase in the amount of extraction force required. A weak extractor grip might hang on to the spent casing only loosely, resulting in a delayed ejection. (For that matter, you could also check the ejector spring.)

    If the ejector doesn't manage to kick the spent casing out in time, then the bolt might stumble on the rim of the new cartridge (or possibly even ride over it completely and hit the base of the body) and push the rear end of the cartridge down, and in doing so cause the nose of the bullet to angle up. The same could happen to the next round in line. The bolt speed is reduced because of the cold and the clumsy feeding, which gives the magazine spring additional time to push up on the next round in the magazine as the bolt is closing. Having been tipped nose up, the bottom round blocks the bolt from going into battery, and the top round slides partway into the chamber through inertia.

    If I were to suggest possible courses of action:

    1. Check extractor springs & check under extractor to make sure nothing is impairing function there.

    2. Check ejector spring tension. If possible, remove ejector and confirm that there's nothing in the channel that's binding it up.

    3. Give the chamber a quick clean. A dirty chamber, especially one with any hard bits inside, will increase the extraction force needed. This shouldn't be the sole cause of the malfunction but it might exacerbate any other problems. Chamber mops are nice for a quick clean, even if they wear out quickly.

    4. You can also give the buffer tube a quick scrub just for insurance's sake. The chamber mop might be handy here again.
    Next time I take it out I will try it with a standard bolt to test this. I had a bad extractor out of the box on the enhanced bolt but never any problems since then. Because both rounds are live, I was dismissing extractor.

    The rifle was not cleaned. I was running out of time and ammo. But, lubrication was reapplied to no success. Original lube was slip 2000 30 weight and Cherry Balmz. Reapplication was just slip 2000 30 weight. I'm going to go back early next week and spend the whole time on diagnosis. It will probably be mid 30's temp wise though.
    Last edited by Hox013; 02-15-20 at 08:38.

  3. #23
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    Regardless of how many mgazines you tried, a double feed is ALWAYS a magazine problem. Try a new a new COLT/NHMTG magazine.

  4. #24
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    Quote Originally Posted by M Sadler View Post
    Regardless of how many mgazines you tried, a double feed is ALWAYS a magazine problem. Try a new a new COLT/NHMTG magazine.
    I deadlined a whole case of those two years ago due to the same problem OP is having.

    Gen M3 Pmags fixed it...

  5. #25
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    Quote Originally Posted by 17K View Post
    I deadlined a whole case of those two years ago due to the same problem OP is having.

    Gen M3 Pmags fixed it...
    An entire case of Okay magazines bad? I personally doubt it, but if that was your experience who am I to argue.

  6. #26
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    Quote Originally Posted by M Sadler View Post
    Regardless of how many mgazines you tried, a double feed is ALWAYS a magazine problem. Try a new a new COLT/NHMTG magazine.
    It wasnt a true double feed because the round wasnt being pulled from the mag by the rear. Just the tip (lol) was popping up onto the chamber area. And very, very highly doubt a gen 3 pmag, 3 Okay Ind. Mags from different production years, and DD 32rd all went bad only in my gun all at once. Trust me, mag is first place I looked.

    I hand cycled a 30rd mag no issues today. I'm hoping Tuesday I can make it back to the range.

  7. #27
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    Probably a crazy thought, but could ice be causing the cartridges to stick to each other? I’m imagining the top round dragging the next one with it....

  8. #28
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    Quote Originally Posted by Curlew View Post
    Probably a crazy thought, but could ice be causing the cartridges to stick to each other? I’m imagining the top round dragging the next one with it....
    Honestly, maybe so... ice chunks were forming on spent casings almost as soon as they hit the snow. I know because I was picking them up to set up malfunction drills. Because I was dropping mags in the snow, perhaps by the time I loaded the mags and set up the drills they began to freeze together. Interesting theory... didnt happen to my buddy that day in his rifle though.

  9. #29
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    Next time I take it out I will try it with a standard bolt to test this. I had a bad extractor out of the box on the enhanced bolt but never any problems since then. Because both rounds are live, I was dismissing extractor.

    The rifle was not cleaned. I was running out of time and ammo. But, lubrication was reapplied to no success. Original lube was slip 2000 30 weight and Cherry Balmz. Reapplication was just slip 2000 30 weight. I'm going to go back early next week and spend the whole time on diagnosis. It will probably be mid 30's temp wise though.
    I wouldn't worry about cleaning the rifle, it should be working even when cold and dirty. In fact I'd probably check that last after all the other steps.

    Another possibility may be that the mag catch is allowing the mag to seat too high. Wear might have loosened tolerances, or perhaps the cold temperatures are locking the mag in when normally it would have wiggled down. To test this out, you could try applying upwards pressure by resting the magazine on a bench, and seeing if you get consistent malfunctions. I'd probably check that after the bolt though just to rule out any extractor or ejector issues.

    Quote Originally Posted by Curlew View Post
    Probably a crazy thought, but could ice be causing the cartridges to stick to each other? I’m imagining the top round dragging the next one with it....
    This could be it.

    Could try testing cold magazines versus a loaded mag that was kept in room temperature conditions to see if there's any difference in function.
    Last edited by LimeSpoon; 02-15-20 at 10:41.

  10. #30
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    Quote Originally Posted by LimeSpoon View Post
    I wouldn't worry about cleaning the rifle, it should be working even when cold and dirty. In fact I'd probably check that last after all the other steps.

    Another possibility may be that the mag catch is allowing the mag to seat too high. Wear might have loosened tolerances, or perhaps the cold temperatures are locking the mag in when normally it would have wiggled down. To test this out, you could try applying upwards pressure by resting the magazine on a bench, and seeing if you get consistent malfunctions. I'd probably check that after the bolt though just to rule out any extractor or ejector issues.
    Good suggestion. I'll try that at home. Cleaning the rifle is the last thing I'll do. If it cant go 1000rds without a deep clean when lube was liberally applied, it's not impressing me.

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