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Thread: Name & Use Of This Part Of Bolt?

  1. #31
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    Quote Originally Posted by polymorpheous View Post
    pulled my BCM bolt.
    it doesn't have the half moon cuts.
    FWIW
    indeed.. my guess is that the half-moon cuts are an FN thing, just like LMT's under-cut lugs are an LMT thing. DD's bolts have the half-moons, and i don't have any proof, but i've been under the impression, or perhaps just the suspicion (and possibly because of this, rather than in spite of it) that they get their bolts from FN.

  2. #32
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    Of course the photo's of the various lugs in this thread show different types of "half moon" cuts.

  3. #33
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    These are the bolts we use at work. No cuts around the lugs.

    Last edited by bo-hoss; 09-01-10 at 20:58. Reason: spelling

  4. #34
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    Quote Originally Posted by patrick sweeney View Post
    I'm not sure I follow. A mil-spec bolt will have a lead-in angle cut on the lug corners, simply as part of the drawings (and for good engineering reasons, to improve reliability and longevity).

    Colt, FN, anyone who makes .mil bolts will have a lead-in cut. The little "tail" cut you see on the bolt body is inconsequential to function or strength.
    Forgive my imprecision.

    Do you know of a commercial bolt with the lead-in cut on the lug corner?
    Do you know of a commercial bolt with the lead-in cut AND the half-moon "tail" cut on the bolt body?
    [EDIT: Nevermind, I think I've found one, complete with half moon "tail" cuts -not milspec but quite reputable.]

    Earlier someone said Daniel Defence bolts had the features characteristic of the FN bolts pictured above. When I look at the images of DD bolts at MidwayUSA(below) and DSG I do not see the lead-in cuts nor the half moon tail cut.
    Last edited by catargadelendaest; 09-04-10 at 04:10.

  5. #35
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    Quote Originally Posted by catargadelendaest View Post
    Earlier someone said Daniel Defence bolts had the features characteristic of the FN bolts pictured above. When I look at the images of DD bolts at MidwayUSA(below) and DSG I do not see the lead-in cuts nor the half moon tail cut.\
    my observations of half-moon cuts come from the ones i've had in my hands, not stock internet photos.

  6. #36
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    Quote Originally Posted by bkb0000 View Post
    my observations of half-moon cuts come from the ones i've had in my hands, not stock internet photos.
    I certainly believe you and I certainly do not think stock photos settle anything.

    I think I'll call DD tomorrow and ask about the characteristics of their bolts. I suspect that lead-in cuts and half-moon reliefs are not as consistently present on their bolts as on FN bolts. If they claim these characteristics are present I may be buying a new bolt tomorrow.

  7. #37
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    Hasn't an industry professional/manufacturer already put this thing to bed in like the 2nd or 3rd post? I'm pretty sure Todd knows what he is talking about.....just saying.

  8. #38
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    OK, to get a grasp of this, you have to know how the bolt is made. The lugs and the barrel extension both have small angle cuts, to ease rotation and locking. That's the little bevel you see on the corner of the bolt.

    When a bolt is machined, it is cut to a certain dimension. Then, after the next step; heat-treatment, the bands behind the lugs (and other areas) are ground to the blueprint dimensions.

    Clearly the machinist figured the "tails" would be cleaned up in the grinding operation. He was wrong, but that doesn't effect the strength of the bolt.

    The "tails" don't effect strength or durability, but I'd be leery of using a "banded" rotation collar bolt in a zombie gun.

    Does it disqualify it for military acceptance? I have exactly that question in to a real-deal .mil bolt maker.
    Last edited by patrick sweeney; 09-02-10 at 14:24.

  9. #39
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    I'll be very interested in what you learn.

    (It almost never hurts to actually improve upon ones understanding of stuff -even if it is of one's understanding of bolt design, manufacture, function, and nomenclature.)

  10. #40
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    The bolt in the picture I posted is not ground after heat treat in any way. The bolt blank is precision turned to +/- .0001 on the critical "band" dimensions. The lug details are milled and then the bolt is sent to heat treat then is either coated with mag-phosphate or hard chrome. Advances in precision turning technology and heat treating have eliminated grinding in some industries. More than one way to skin a cat...

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