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Thread: BCG Cut-Away

  1. #1
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    BCG Cut-Away

    Looking for an image of a BCG cut-away showing the 3 bore.
    Wondering how critical is the bolt tail seal?
    You won't outvote the corruption.
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  2. #2
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    Quote Originally Posted by prepare View Post
    Looking for an image of a BCG cut-away showing the 3 bore.
    Wondering how critical is the bolt tail seal?
    The fit there is held pretty tight; if we talk about it as a gap all the way around it's held to min. .0004 per side to max .0012. I have seen all of one that, between wear and/or parts that were maybe out of tolerance to start with, it leaked enough gas there to be a stand-alone problem.

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    Quote Originally Posted by Ned Christiansen View Post
    The fit there is held pretty tight; if we talk about it as a gap all the way around it's held to min. .0004 per side to max .0012. I have seen all of one that, between wear and/or parts that were maybe out of tolerance to start with, it leaked enough gas there to be a stand-alone problem.
    Thanks for the clarification.
    This provides some context as to why it’s not a good idea to aggressively over clean the bolt tail area.
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    This is a crop from an old blueprint for the carrier. You can see the tight tolerances down to +/- .0003 in addition to the true position callouts and surface finish requirements.

    Interestingly, the .5315 diameter calls out a .0010 tolerance, but the tolerance block on the drawing doesn't have a value for a four place decimal. Gotta love engineers.


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    That bolt tail seal is probably the most critical dimension on the whole carrier.

    It's also the worst offender area for out of spec with lower quality units.

    Quote Originally Posted by prepare View Post
    Thanks for the clarification.
    This provides some context as to why it’s not a good idea to aggressively over clean the bolt tail area.
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  6. #6
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    Quote Originally Posted by Clint View Post
    That bolt tail seal is probably the most critical dimension on the whole carrier.

    It's also the worst offender area for out of spec with lower quality units.

    Some people need to read that twice and let it sink in.
    Stick


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    Quote Originally Posted by prepare View Post
    This provides some context as to why it’s not a good idea to aggressively over clean the bolt tail area.
    Interesting. I've never given bolt tail seal much thought. I've seen that the metal doesn't foul there however. I used to clean my bolt tails very aggressively and never had an issue.
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    Check out the sotar school of the American rifle on u-tube for great gauge ideas

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