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Thread: Full Auto Malfunction PITA

  1. #31
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    Bolt bounce is generally from over-gassed and or under buffered rifles with carbine gas. The bolt and carrier velocity are too high. The malfunction is, hammer down, live round in the chamber with light primer strike while shooting auto.


    When the bolt goes into battery the carrier stops against the barrel extension. If the carrier is going too fast it will bounce back off the barrel extension and unlock or partially unlock the bolt before going back into battery. The firing pin will not contact the primer enough to set it off unless the bolt is locked. Timing is also a factor, the hammer has to fall when the bolt is unlocked.

    The buffer plays a big part in this and you have to understand that it is more than a static "weight"
    The floating weights in a buffer work to keep the carrier from bouncing off the rear of the buffer tube with as much force, thus reducing the forward speed.

  2. #32
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    Todd,

    So I basically I was correct. These carbines were working fine, but the gas port has more than likely eroded and now we are starting to see the effects. Now my guess would be that a heavier buffer would fix it but it would be a "band-aid" as others have said because the erosion will continue? Does that about sum it up?

    Quote Originally Posted by Todd.K View Post
    Bolt bounce is generally from over-gassed and or under buffered rifles with carbine gas. The bolt and carrier velocity are too high. The malfunction is, hammer down, live round in the chamber with light primer strike while shooting auto.


    When the bolt goes into battery the carrier stops against the barrel extension. If the carrier is going too fast it will bounce back off the barrel extension and unlock or partially unlock the bolt before going back into battery. The firing pin will not contact the primer enough to set it off unless the bolt is locked. Timing is also a factor, the hammer has to fall when the bolt is unlocked.

    The buffer plays a big part in this and you have to understand that it is more than a static "weight"
    The floating weights in a buffer work to keep the carrier from bouncing off the rear of the buffer tube with as much force, thus reducing the forward speed.
    Last edited by Iraqgunz; 07-17-09 at 11:43.



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  3. #33
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    I'd just replace the bolt and barrel. A more difficult fix which requires some machinery is to drill the gas port out and install a 4-40 set screw drill through it using a 1/16" drill bit (this will be .0625"). If the port is that eroded the barrels throat may be eroded too making for bad accuracy.

    Randall explained the fix here in this thread.

    I have access to a few milling machines and lathes and I doubt I would even try this unless I owned the barrel.
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  4. #34
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    Quote Originally Posted by Todd.K View Post
    Bolt bounce. In auto, hammer down, light primer strike.

    What buffer does it have?

    This is a good thought I think. Since BM barrels use gas ports that are HUGE, an h3 buffer and a stiff carbine spring would help/fix.

    My theory though is that since gas ports erode quickly and this weapon most likely has some rounds through it, that an H3 will not be able to save it.


    C4

  5. #35
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    I have already proposed that we start buying more barrels and an probably going to buy a handful of H2/H3 buffers as well. Thanks for the all the info and input.



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  6. #36
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    Quote Originally Posted by Iraqgunz View Post
    I have already proposed that we start buying more barrels and an probably going to buy a handful of H2/H3 buffers as well. Thanks for the all the info and input.
    Let me know. We can get you BCM stripped barrels and stock mil-spec H2 and H3 buffers.


    C4

  7. #37
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    Your ears must have been burning. If BCM has the gas block configuration we need I most certainly will even if they are a little more than what we paid for the BM barrels.

    Quote Originally Posted by C4IGrant View Post
    Let me know. We can get you BCM stripped barrels and stock mil-spec H2 and H3 buffers.


    C4



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  8. #38
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    Quote Originally Posted by C4IGrant View Post
    This is a good thought I think. Since BM barrels use gas ports that are HUGE, an h3 buffer and a stiff carbine spring would help/fix.

    My theory though is that since gas ports erode quickly and this weapon most likely has some rounds through it, that an H3 will not be able to save it.


    C4
    H3 on a new barrel?? Theyre that big?

  9. #39
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    Quote Originally Posted by gotm4 View Post
    I'd just replace the bolt and barrel. A more difficult fix which requires some machinery is to drill the gas port out and install a 4-40 set screw drill through it using a 1/16" drill bit (this will be .0625"). If the port is that eroded the barrels throat may be eroded too making for bad accuracy.

    Randall explained the fix here in this thread.

    I have access to a few milling machines and lathes and I doubt I would even try this unless I owned the barrel.
    Ive seen this fix done before on a pistol but does it last?

  10. #40
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    If you don't mind an aside. . . .

    Just wondering, but would it be possible to test for an eroded/enlarged gas port by measuring the velocity of the bullet? Would the larger volume of gas going through the port lower the velocity of the bullet relative to a properly sized port, or are we talking such a small amount of difference that you couldn't measure it given the inconsistency of the ammo?

    I have very little technical knowledge of the platform, so I apologize if the question is misplaced and also for not offering any real input to the discussion. I was just wondering after reading through the thread.

    Jason
    Last edited by bulbvivid; 07-17-09 at 21:16.

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