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Thread: SureFire Bolt Carrier Group Analysis

  1. #11
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    Where is the highest stress on the bolt from the cam pin? I guess thatís really the more important question because Iíve seen a bolt broken by the cam pin, but never seen a broken cam pin.

  2. #12
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    This is all really good information lysander. Thank you.

    Joe Mamma
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  3. #13
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    Quote Originally Posted by Todd.K View Post
    Where is the highest stress on the bolt from the cam pin? I guess that’s really the more important question because I’ve seen a bolt broken by the cam pin, but never seen a broken cam pin.
    The highest stress in the bolt from the cam pin is where there is the least material, the two webs either side of the cam pin hole, even more specifically at the top of those webs. The cam pin does two things, it places a longitudinal load on the bolt, stretching it, and it tries to rotate, placing a bending load at the webs.

  4. #14
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    Where in the unlocking cycle is the highest stress on the bolt at the cam pin hole?

    This seems like the low hanging fruit of adjusting the cam pin slot to me. Actually reducing a known failure point.

  5. #15
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    Apparently CAG (Delta, or whatever they go by now) had *supposedly* adopted this BCG and the Geissele SD-ish platform for acquisition a year or so back to replace their HK416's. Not sure how far along in the pipeline they are though. The BCG itself is unobtanium vaporware, and has been for quite some time.....unless you want to drop $800+ for one on Gunbroker.

    I would assume our tip-of-the-spear folks would have done testing, especially given that it was a BCG from one maker and the carbine from another; I have to admit that this was an unusual combo given the Geissele REBC that usually comes with the gun.

    Any thoughts Lysander?
    Last edited by ABNAK; 01-22-23 at 21:32.
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  6. #16
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    Quote Originally Posted by Todd.K View Post
    Where in the unlocking cycle is the highest stress on the bolt at the cam pin hole?

    This seems like the low hanging fruit of adjusting the cam pin slot to me. Actually reducing a known failure point.
    If I had to guess, likely incorrectly, I would wager it is the moment the cam pin bottoms out in the forward extent of the cam pin track (initiation of rearward bolt movement, after rotational unlocking).

    But, that's literally just a guess. Will defer to Lysander or Constructor.


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  7. #17
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    Quote Originally Posted by BufordTJustice View Post
    If I had to guess, likely incorrectly, I would wager it is the moment the cam pin bottoms out in the forward extent of the cam pin track (initiation of rearward bolt movement, after rotational unlocking).

    But, that's literally just a guess. Will defer to Lysander or Constructor.


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    That is where the highest loads are on the cam pin and the hole it is in. The entrance to the cam angle is not a very highly loaded area, as the only loads are from sliding friction of the cam pin on the side of the path, the friction of the bolt in the carrier and the inertia of the bolt. And in order to make any large changes to that radius, you have to increase the actual cam angle, which start to negatively effect the bolt carrier velocity.

    I just thought as the only time anyone actually altered the carrier geometry (to my knowledge), i thought it would be interesting to examine. There probably is some merit to the idea.

  8. #18
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    How does the cam path compare to the one in LMT enhanced carrier? Does it have the same issue with regards to the gas rings?

    The LMT carrier allows the bolt to travel farther forward. In fact, there is a protruding collar on the front of the carrier to retain the extractor pin as captive beyond the normal travel of the bolt.

  9. #19
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    Quote Originally Posted by Heavy Metal View Post
    How does the cam path compare to the one in LMT enhanced carrier? Does it have the same issue with regards to the gas rings?

    The LMT carrier allows the bolt to travel farther forward. In fact, there is a protruding collar on the front of the carrier to retain the extractor pin as captive beyond the normal travel of the bolt.
    Essentially doesn't matter as they are unobtanium.
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  10. #20
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    Quote Originally Posted by ABNAK View Post
    Essentially doesn't matter as they are unobtanium.
    FCD has complete E-BCGs in stock right now. I bought one a few months ago too. They havenít been that hard to find.


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