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Thread: Phosphate under gas block

  1. #101
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    Quote Originally Posted by Failure2Stop View Post
    I hate to answer a question with a question, but are you saying that Colt does not?
    I do not know how Colt makes their bolts so I am making assumptions - but it would be too expensive for them to test each bolt for each dimension on the manufacturing drawing. They would have to CMM each bolt - and that takes a while - so the normal thing to do is a statistical sampling on a CMM. Then there would be gauge points and an inspection drawing for the most common areas, so some or all of those areas would be checked for each one.

  2. #102
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    Quote Originally Posted by rsilvers View Post
    I do not know how Colt makes their bolts so I am making assumptions - but it would be too expensive for them to test each bolt for each dimension on the manufacturing drawing. They would have to CMM each bolt - and that takes a while - so the normal thing to do is a statistical sampling on a CMM. Then there would be gauge points and an inspection drawing for the most common areas, so some or all of those areas would be checked for each one.
    I was more talking about HPT/MPI, as it does a pretty good job of illustrating issues quickly.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  3. #103
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    Quote Originally Posted by Failure2Stop View Post
    This test could easily be passed without ever staking the key, so I am not all that convinced that the test proposed proves anything useful.
    Maybe it does not prove anything useful in the field, but the torque test would prove that it meets the military requirements for coming-undone-ness - and was properly staked.

  4. #104
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    Quote Originally Posted by Failure2Stop View Post
    I was more talking about HPT/MPI, as it does a pretty good job of illustrating issues quickly.
    That test is next to useless because essentially all bolts pass it, and a tougher test would be too destructive. Many of us have bolts in our ARs right now with thousands of rounds on them that would fail MPI if tested today, yet we still keep them in our rifles. AR bolts crack with use - they just do. We know today, but maybe not 50 years ago, what that means in real-world terms - that the bolt should be replaced at 5000 rounds for super hard use, or 10,000 rounds for typical use, or when it fails if we don't really care.

  5. #105
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    Quote Originally Posted by Failure2Stop View Post
    Just spring or spring and buffer?
    I am asking if you think that an original M16 rifle spring, with an o-ring, and an insert - would have too much extraction force on an M4. Or if you just meant that that combination with a spring that was not an original M16 rifle spring would have too much force.

  6. #106
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    Quote Originally Posted by Failure2Stop View Post
    I was more referring to the assertion that HK and FN intentionally modified their submissions.
    I would not use the term modify. HK had to build their XM8s for the test. They don't just have XM8s sitting around in inventory. Colt was the only party that did not have an opportunity to provide rifles.

  7. #107
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    I'm not sure why you're placing so much emphasis on CMM.

    With the precision of modern manufacturing, the likelihood of a bolt being made that fails to meet dimensional specs is very unlikely. Factory test firing should reveal any major discrepancies anyway.

    Obviously, HPT and MPI are a bit dated, and the notion that they might as well not be performed at all does have some merit. The idea being that any bolt that fails MPI when it is new is not going to last longer than a thorough test firing anyway.

    The concern I have heard more often is that the heat treatment of a bolt can be too deep, causing it to be brittle. It won't be cracked, so won't fail MPI right away, but could break unexpectedly a few hundred rounds later. That is what concerns me- and is why I don't place nearly as much emphasis on HPT/MPI as I do trust in the company. For example, LaRue doesn't HPT or MPI, but I would probably use one of their bolts.

  8. #108
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    CMM as opposed to measuring another way? It is just easier/faster.

    I think a part failing a dimensional check is about 10000 times (literally) more likely than a part failing MPI - yet some demand the MPI and don't demand the other. All of the MPI QC budget should go toward doing more useful checks.

    I highly doubt LaRue does their own heat treat. They almost certainly send it to a heat-treat facility - just like everyone else.
    Last edited by rsilvers; 12-08-11 at 12:53.

  9. #109
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    Quote Originally Posted by rsilvers View Post
    CMM as opposed to measuring another way? It is just easier/faster.

    Lamarbrog - I highly doubt LaRue does their own heat treat. They almost certainly send it to a heat-treat facility - just like everyone else.
    Not so much the method- the process entirely. If the bolt fits, and passes test firing- the dimensions are probably good. Something being dimensionally wrong with a bolt is so far down on the list of things I worry about...

    And I doubt LaRue does their own heat treating, too. But they likely contract it out to a reputable heat-treat facility, because they have a reputation for quality to uphold. Bushmaster and DPMS don't really have that same reputation.

  10. #110
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    Quote Originally Posted by rsilvers View Post
    CMM as opposed to measuring another way? It is just easier/faster.
    specifically designed go/no-go gauges would also work, depending on the tolerance. it's quicker than a CMM and doesn't require a person trained on the machine.

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