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Thread: HPT and MPI: still viable and necessary or outdated bureaucracy?

  1. #101
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    Quote Originally Posted by orionz06 View Post
    I do think that skipping the HPT/MPI also comes with skipping the correct material or other steps along the way, so it is tough to 100% pinpoint the real problem. All we know is that the right material and right tests yield really good bolts.
    and I think that it was mentioned elsewhere that part of the rationale is simply keeping everyone honest.

    There is a lot to the matieral issue, and the new Chart includes a section for material. If some of the lower-cost brands would actually answer me back instead of sticking their heads in the sand it would be helpful.

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    Quote Originally Posted by 12gauge View Post
    SO WRONG! I assure you that a MTR(material test report) does not mean shit after you machine and proof test your bolt. Even if the material was inspected(typically ultrasonics) it means nothing more than the material was sound before you machined it and overpressure tested it.
    You are correct but I was only responding to his mention of trying to detect voids in the metal.
    Last edited by rsilvers; 05-18-11 at 08:46.

  3. #103
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    Quote Originally Posted by rob_s View Post
    If, as you say, nobody is dimensionally checking their bolts, and if, as you imply, a dimensionally incorrect bolt is a problem, we would be hearing about mass failures due to.. well due to whatever the specific failure is that this would induce. But we don't.

    What we do hear about, all the time but less so recently, is bolts cracking. Miraculously as it turns out, when any one brand has had an epidemic of cracking bolts it turns out to be a company that is not HPT/MPI. Do all companies that skip HPT/MPI have massive failures? No, but to this point every company I've ever heard of with massive failures has been one that skipped the process.
    Part 1 - we do hear about unreliable ARs often. This is going to be out of spec parts.

    Part 2 - AR bolts crack from improper heat treat, materials, machining, and just from normal use after so many rounds. The best way to screen for that is to use the proper materials, check hardness, and use the proper minimum radius on the tooling.

  4. #104
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    Quote Originally Posted by rsilvers View Post
    Part 1 - we do hear about unreliable ARs often. This is going to be out of spec parts.
    Correct, but is it more often the bolt or the gas port, buffer weight, carrier weight, crooked gas block, and extractor spring, or is it a dimensionally incorrect bolt?

  5. #105
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    Quote Originally Posted by orionz06 View Post
    This can be troublesome when a shop is trying to stretch out their tooling to last a bit longer.

    But to what you said earlier, is there any good data on parts failures? Amount of hammers that fail, pins that fail, etc?

    I have no problem accepting that the HPT/MPI might not be necessary if Colt/BCM/Daniel Defense/TDP Maker X tells me that they have never seen a bolt fail after the HPT, but I would certainly still pursue parts that were HPT/MPI. I was told a little bit ago that there was not a 100% pass rate after HPT, hence my stance on the issue.
    I can't repeat any data I have from the major makers. But I agree with you, if the number of failures is significant, then you would want this test - at least on the bolts made by those makers.

  6. #106
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    [QUOTE=orionz06;1001190]I do think that skipping the HPT/MPI also comes with skipping the correct material or other steps along the way/QUOTE]

    So you are saying that HK does not likely use good steel, because they don't do MPI? The Sig 550/551 does not likely use good steel? The G36 does not? The KAC? AAC bolts are then not likely C158 like we say?

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    Quote Originally Posted by rob_s View Post
    and I think that it was mentioned elsewhere that part of the rationale is simply keeping everyone honest.
    But it does not because they can cheat on the test. You have to do your own testing on your vendor's parts.

  8. #108
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    Quote Originally Posted by orionz06 View Post
    Correct, but is it more often the bolt or the gas port, buffer weight, carrier weight, crooked gas block, and extractor spring, or is it a dimensionally incorrect bolt?
    All sorts of parts that could be out of spec. Which is why I am saying that because a QC and QA budget is finite, I would rather spend that budget looking for parts that lead to the most problems. MPI is far from the most dollars/problem-locating ratio.

    I know someone said - "Well, do as many dimension and heat-treat checks as the budget allows, but then also do a $10 MPI check of the bolt, and pass that along to the consumer." But why pick that check other than marketing reasons? Why not also X-ray the trigger parts? What makes you pick one test vs the other? In the end, you have to leave it to the engineers and QC/QA people to look at which parts fail the most and cause the most problems, sort them by priority, and do those tests until the budget is gone.

    It seems like the general summation of what we have discussed is that perhaps MPI does not matter, but those who don't do it tend to skip all sorts of other important things such as using C158. That is actually true. Then you give a pass to Hk and KAC, because they are awesome and you know they use good materials. That is also actually true.

    But you also have to be open to the possibility that someone could skip all sorts of important stuff, and do the MPI test just to get a good rating on the chart. I know we spend closer to $50 than $10 on QC/QA, so someone could save money by doing MPI and not a lot of gauging. It is obviously much easier to market that your rifle company does MPI than to quantify how much gauging is done.

  9. #109
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    Quote Originally Posted by rsilvers View Post

    So you are saying that HK does not likely use good steel, because they don't do MPI? The Sig 550/551 does not likely use good steel? The G36 does not? The KAC? AAC bolts are then not likely C158 like we say?


    No, the opposite in fact. Their track record of making good guns (I know little of the 550/551 though) is enough to give them a pass, in my eyes. If you look at post #27 I say just that.

    Quote Originally Posted by rsilvers View Post
    But you also have to be open to the possibility that someone could skip all sorts of important stuff, and do the MPI test just to get a good rating on the chart. I know we spend closer to $50 than $10 on QC/QA, so someone could save money by doing MPI and not a lot of gauging. It is obviously much easier to market that your rifle company does MPI than to quantify how much gauging is done.

    It is quite possible to check tons of boxes and still not make a good gun. It is also possible to make a good gun that has very few checks on the chart. I think we are really on the same page here, but we have different sets of info that lead to our different positions. You do need to accept the fact that I am by no way suggesting that poorly sized parts are acceptable. As it stands, right now, with whatever pretend secret info I may or may not have been told, I cannot see a valid reason to skip the HPT/MPI on a standard M16 bolt. I am not locked into this position, but I don't think anyone is going to send me a PM or email with stats on production runs of their parts, so it is unlikely for my position to change.

    And realistically, the price between a crappy bolt and a good one is insignificant once I start factoring in actually paying to shoot the gun, so....
    Last edited by orionz06; 05-18-11 at 09:29.

  10. #110
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    Quote Originally Posted by orionz06 View Post
    No, the opposite in fact. Their track record of making good guns (I know little of the 550/551 though) is enough to give them a pass, in my eyes.
    So would you be comfortable if say, Colt told you HPT/MPI was not needed and dropped it on non military rifles?

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