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Thread: Name & Use Of This Part Of Bolt?

  1. #41
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    Quote Originally Posted by catargadelendaest View Post
    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.
    I spoke to DD tech support today. We had the DD website pic of bolt asembly ( http://www.danieldefense.com/?page=s...product_id=153 )in front of us and he had their DD bolt assembly in hand.

    He told me that the right and left rear corners of the lugs were the same, square, one was the mirror image of the other. From this I gather that the one in his hand had no lead-in cuts.

    I also asked specifically about the shelf immediately behind the lug, parrallel to lug. (Recall, immediately behind each lug is a little shelf parrallel to the lugs. There are also parrallel troughs between each lug. These troughs run the length of the lug and the little shelf immediately behind each lug (extractor aside).) He told me that the shelf immediately behind the lug had no slash marks, no semi-elliptical or half-moon cuts.

    From this conversation with DD I deduce that not all DD bolts have the lug area characteristics of an FN bolt. I presume and believe that DD sells a mighty fine bolt because they are generally known to make and to sell good stuff.

    I did not ask about the details of their procurement and manufacuring processes.
    Last edited by catargadelendaest; 09-03-10 at 15:20. Reason: Update

  2. #42
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    Quote Originally Posted by TY44934 View Post
    More oddities noticed:

    1) Why are the letters "MPC" tilted on some bolts, but not others?

    2) Why is the raised ridge between the cam pin hole and the letters MPC apparently flutted on some bolts, but not on others?
    #2, EXCELLENT QUESTION!
    Additionally, what is the name of that circumferential ridge and the name of the apparent fluting?

    Is "rib" the actual name of the circumferential ridge; is it "bearing band"; what is it's name?
    Is the apparent fluting just the result of sloppy machine work?
    Last edited by catargadelendaest; 09-03-10 at 15:12.

  3. #43
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    Quote Originally Posted by polymorpheous View Post
    pulled my BCM bolt.
    it doesn't have the half moon cuts.
    FWIW
    I'll bet a chocolate glazed donut that the left rear corners of the lugs on your BCM bolt have a distinct radius milled into them that the right rear corners do not have. If so, would it not be accurate to call this feature the "BCM-like radial lead-in surface?"

    Also, it begs the question, in what circumstance is each preferable? When is it most preferable for the left rear corner of the lug to have a relatively square lead in surface, to have a "BCM-like radial lead-in surface", and to have a bevelled lead-in angle surface (like a presumed milspec requirement).
    Last edited by catargadelendaest; 09-03-10 at 16:34.

  4. #44
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    Quote Originally Posted by Iraqgunz View Post
    I have seen Colt bolts with other types of MP markings. I believe some were MPJ and MPY. I would say that some of those are possibly FN and maybe LMT.

    The Colt bolt with a MPXC marking where X can be an alphabet letter designates a date code and has nothing to do with LMT or FN.
    "Not every thing on Earth requires an aftermarket upgrade." demigod/markm

  5. #45
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    Man,and I thought I had a BCG fetish.

    My small sample size of three in hand DD bolts purchased in the last year(one individual and two from complete XVM4's) do not have the "half moon" cuts in the ridges at the rear/root of the lugs.They all do have the "lead in" cuts on the left rear of the lugs.Very finely machined too I might add.
    Its my understanding that the DD bolts and carriers are made by AO and are assembled at DD,but Ive never been able to verify that information so take that for what its worth..

    Furthermore,I also have one BCM,two Armalite bolts,and they are identicle to the DD in as far as how the area in question is machined.
    My LMT bolts(sample size of four) have the recessed lugs and are smooth without the raised ridges running from the root of the lugs rearward.
    Last edited by Blankwaffe; 09-03-10 at 19:52.
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  6. #46
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    Hmmmm, interesting....

    And my .mil manufacturer tells me they are "not to print" but that if you try hard enough you could find a government inspector who would declare them OK.
    Last edited by patrick sweeney; 09-08-10 at 17:00.

  7. #47
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    I have been told they are 'relief cuts' to prevent fatigue and bolt lug shear. I unfortunately cannot remember which source told me this, I will do a little research and try and get back with a more definitive (i.e. with some backup proof) answer.

    Dawg

  8. #48
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    Plot thickens (from TOS):

    http://www.ar15.com/forums/topic.html?b=2&f=27&t=193736

    semi-circles = tool path cutouts for lug radius. According to Armalite anyway.

  9. #49
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    Quote Originally Posted by TY44934 View Post
    Plot thickens (from TOS):

    http://www.ar15.com/forums/topic.html?b=2&f=27&t=193736

    semi-circles = tool path cutouts for lug radius. According to Armalite anyway.
    Thanks for the reference to Armalite input.
    Note, Todd K. of Noveske Rifleworks pointed out the same thing with regard to the analogous slash marks on Colt bolts in pg. 1 of this thread, second response.
    Last edited by catargadelendaest; 09-15-10 at 13:16.

  10. #50
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    Quote Originally Posted by catargadelendaest View Post
    Thanks for the reference to Armalite input.
    Note, Todd K. of Noveske Rifleworks pointed out the same thing with regard to the analogous slash marks on Colt bolts in pg. 1 of this thread, second response.
    Todd K. of Noveske is the first to hit the nail on the head. My conversation with FN since my last posting confirms Todd K.'s assertion.

    Additionally, the FN depressions (and hence the Colt slash marks) behind the bolt lugs serve no other utilitarian function in the operation of the weapon.

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