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Thread: Potential problem with GTS Thunderbolt BCG

  1. #1
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    Potential problem with GTS Thunderbolt BCG

    The upper is a 14.5 inch BCM middy, lower is a LMT. The problem is that on the last round the carrier engages the bolt catch/release and not the bolt. The last round is fired, empty brass will eject, BCG will be held back just not by the bolt. This happens with USGI mags, pmags, and it happens with 4 different lowers. Ammo was TAP, buffer was H2.
    When I put in an old Bushmaster carrier this did not happen. If I manually cycle the action with the thunderbolt I can make it happen. When I manually cycle the action with a different carrier I can not. Will this problem go away with more trigger time? Should I try stoning an area of the carrier and if so where?
    If this seems like a problem with the carrier to you guys I will contact the manufacturer, if not let me know what you think. Thanks.

  2. #2
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    check the gas rings. Does the GTS BCG pass the gas ring test (placing it bolt0down on the table and seeing if the weight of the carries compresses the bolt. Further, look at the rings and see if they are worn.

    I would still rec contacting GTS; Denny is usually really good about working through these issues. I mean, you haven't assembled a gun show special...you're using quality components from different makers. Talk to Denny.

  3. #3
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    The gas rings are GTG. This is a new BCG. I will contact them next week. Thanks.

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    I'm confident Denny will diagnose/rectify the issue.

    Also, how many rounds do you have through the upper?

    I have a BCM 14.5" w/ FSC556 that runs great now...but the first 100 rounds or so were a BITCH. It didn't cycle very well then.

    I think it may need to wear-in slightly.

    For the last 300, it eats tula .223 for breakfast/lunch/dinner and runs like a sewing machine. It's on its way to be GTG now.

    Just thinkin' out loud here....

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    why not just dip back to an H buffer? simple, simple fix.

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    Quote Originally Posted by bkb0000 View Post
    why not just dip back to an H buffer? simple, simple fix.
    Yeah I was kind of thinking that might work, but why does the carrier engage the bolt release when I manually cycle it with the thunderbolt, but not with any other carrier I try?

  7. #7
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    guess i missed that part... mayhaps there's something wrong with the thunderbolt carrier. i've never even heard of 'em- are they something special?

  8. #8
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    Quote Originally Posted by greene View Post
    Yeah I was kind of thinking that might work, but why does the carrier engage the bolt release when I manually cycle it with the thunderbolt, but not with any other carrier I try?
    Make sure you don't have a foreign object down in your buffer tube limiting travel like a piece of a rag or a patch.
    My brother saw Deliverance and bought a Bow. I saw Deliverance and bought an AR-15.

  9. #9
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    Admittedly I know jack about this BCG. I did however test one of BCM's 14.5" midlengths along with markm. I don't think that you need an H2 buffer. An H should be more than adequate. Although IIRC in our testing we even used an H3.

    My guess is that something is wrong with the BCG. I say use a standard one and your problems will more than likely disappear.



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  10. #10
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    Im having a hard time picturing exactly what you are trying to describe is happening. I am curious which portion of the carrier the bolt catch is locking back on. Pics would be helpful.

    From what I can gather, it sounds like your "Thunderbolt" might be a Full Auto carrier and the Bushmaster carrier you tried is a Semi Auto carrier? Possibly the heavier weight of the Full Auto carrier, in-conjunction with the H2 buffer and your ammo combo is "short-stroking" the carrier just enough to make the bolt catch to snag on the leading face of the bottom of the carrier instead of on the bolts face???

    Maybe try running an "H" buffer instead of the "H2" and see what happens.
    Last edited by nickdrak; 10-10-10 at 04:33.

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