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Thread: What could make a semi fire a burst?

  1. #1
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    What could make a semi fire a burst?

    I witnessed a semi-auto Bushmaster go 3 round burst the other day. It fired a 3 round burst on the shooter, then as they had a moment of "wtf!?" and began to remove the gun from their shoulder and set it down...it fired off another round.

    The shooter was a Marine who exercised good trigger finger discipline when I observed him (I was the RO). He swears he didn't pull the trigger and the gun fired on his own, and I'm inclined to believe him. I witnessed the gun fire the 3 round burst, and it wasn't just him shooting fast. I know the difference between someone with a fast finger vs. auto fire.

    I ripped the gun open thinking the disconnector was bad...it looks almost new.
    It has about 1/16"-3/32" of positive engagement with the hammer, and positively engages the sear upon reset. Nothing is chipped/ worn.

    The BCG is semi, the hammer is semi, the selector is semi, the disconnector is milled to be semi, the trigger is auto style. I couldn't find ANYTHING wrong inside the gun.


    I'm stumped...anyone have any idea how could something like this could happen?

  2. #2
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    seized firing pin?

  3. #3
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    I'd definitely tell that Devildog not to take it back out to shoot until it's fixed. It would suck to get hemmed up by having a "machine gun".

  4. #4
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    Quote Originally Posted by Kimbo View Post
    I'd definitely tell that Devildog not to take it back out to shoot until it's fixed. It would suck to get hemmed up by having a "machine gun".
    It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.

    None the less, I want to get this thing figured out, pronto.

    Will check the firing pin out....don't know why I didn't think of that.

  5. #5
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    how many rounds has the weapon seen? if the firing pin checks out, i wouldn't bother trying to single out any one component.. i'd probably just go ahead and replace the whole FCG and cover all my bases

  6. #6
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    Quote Originally Posted by CoolBreeze View Post
    It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.
    Nice
    I agree with BKB and replace everything. Once one part starts others are sure to follow.

  7. #7
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    Possible unintentional bump-fire?

  8. #8
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    Make sure that you have a semi-auto selector lever and not a full-auto selector lever in the weapon. Also, check the disconnector and spring as I believe that is where your problem lies. A few things to ask yourself.

    1. Who assembled the weapon and what parts were used?

    2. How many rounds have been put through the weapon?

    Though you say you checked already and I believe you these are the only plausible reason that I can think of.

    Quote Originally Posted by CoolBreeze View Post
    It's a rental...and we have all kinds of paperwork when it comes to doing class 3 stuff, including the manufacturing license, IIRC.

    None the less, I want to get this thing figured out, pronto.

    Will check the firing pin out....don't know why I didn't think of that.
    Last edited by Iraqgunz; 04-23-09 at 08:55.



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  9. #9
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    Could be worth while to check the buffer detent and buffer spring as well to make sure they are performing properly.

  10. #10
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    Quote Originally Posted by DRich View Post
    Possible unintentional bump-fire?
    That's what I was thinking.
    Back in the land of Waffle House and sweet tea!!!

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