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Thread: Some notes on HPT/MPI

  1. #11
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    It really comes down to trust and reputation of the manufacture. Anyone can say (and many do) that their product are milspec but how can one verify there claim? The military has the luxury of having someone looking over the shoulder of the manufacture making sure that that they are in compliance.

  2. #12
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    I distrust any blanket "milspec" claim. If you look at the way BCM lists out their products they say exactly what specs it is they are conforming to, not just simply saying "milspec".

    We addressed this in the Chart early on when the discussion turned to the term and it was generally agreed that it would be best to take the specs one by one and remove any mention of "milspec" or "TDP" from the Chart. When I wrote the Explanation of Features I tried to keep that same idea in mind and explain why a particular item, from the spec, was desirable.

    Obviously it still does come down to the trust issue. With consumers becoming more educated terms like "HPT" and "MPI" have replaced the blanket "milspec", but many people throwing around the terms don't now what HPT really is any more than they knew what milspec really was.

    Which is part of the intention of this thread, to get out there the information and where to find it for those that care to know the gritty details.

  3. #13
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    MIL-STD-1949A lists several ASTM standards as references and includes them in the standard. Some interesting things when you start burrowing into that...

    ASTM E1444-01 "replaces MIL-STD-1949" but is superseded by ASTM E1444-05. ASTM E1444-05 references ASTM A275 "Standard Practice for Magnetic Particle Examination of Steel Forgings", which also appears in MIL-STD-1949.

    Confused yet? I'm getting there!

  4. #14
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    Can anyone give a reasonable estimate regarding what percentage of barrels don't pass HPT?
    Or, what % can be expected to fail, more or less?
    Last edited by BudJr; 03-30-10 at 03:37.

  5. #15
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    Quote Originally Posted by BudJr View Post
    Can anyone give a reasonable estimate regarding what percentage of barrels don't pass HPT?
    Or, what % can be expected to fail, more or less?

    ***This is speculation***

    I would guess that the HPT is looking for either bad raw materials or bad heat treat. The percentage of failures would probably be very low. To me this would mean below .5% If a bad batch of barstock or improper heat treat makes it that far, I would expect high failure rates, as in over 10%.

    Any manufacturer that is going through the trouble of doing those tests (Colt, BCM, Noveske...) is buying premium raw materials, and the instances of substandard bars should be rare. I can easily envision entire batches of barrels going through test with zero failures.

    I'm a metallurgical engineer with some barstock experience in shafts for high-horsepower transmissions (up to 3000 hp), and in government specifications. That experience with high quality barstock is what I based my SWAG on.

    Maybe we can get one of the manufacturers to chime in with real data.

  6. #16
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    Bud, just to be clear the part does not fail HPT. HPT is used to stress the part, and then MPI is the pass/fail.

    I know of no manufacturers that are willing to release the percentage of failure information publicly.
    Last edited by rob_s; 03-30-10 at 11:11.

  7. #17
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    Quote Originally Posted by hikeeba View Post
    Sorry. I must have misremembered what I read. That is also stated word for word in MIL-R-63997B (AR) for the M16A2.



    Just because something is stated as being 'mil-spec,' doesn't necessarily mean it adheres to the exact military specification for that item. And even though a manufacturer states it's product has been HPT and/or MPT, it doesn't necessarily mean that those proceedures were carried out in accordance with a military standard.

    I understand what the military specifications are and why they are in place. I also feel the term 'mil-spec' is used quite loosely in the consumer market. 'Mil-spec' in that the bolt has been properly manufacturer, tested, but mysteriously not marked? Or 'mil-spec' in that it was made to a standard dimension and will work with 'any mil-spec' carrier?


    Correct. Everyone from BM to Oly uses the term "Mil-Spec." When they use it, they mean that all parts will FIT together. So you can take their upper and stick it on an M4. So in their little minds, they ARE Mil-Spec.

    The next question that should be asked when companies say that they HPT/MP is, what are your exit criteria from the MP test? What is acceptable and what isn't?



    C4

  8. #18
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    Quote Originally Posted by BudJr View Post
    Can anyone give a reasonable estimate regarding what percentage of barrels don't pass HPT?
    Or, what % can be expected to fail, more or less?
    From conversations I have had with various companies, I would say that they failure rate is around 3%.


    C4

  9. #19
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    Quote Originally Posted by rob_s View Post
    Bud, just to be clear the part does not fail HPT. HPT is used to stress the part, and then MPI is the pass/fail.
    Yes. I should have been more clear.

    That's what I get for trying to respond in a hurry.

  10. #20
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    BCM seems to be straight forward about what they do.
    HPT / MP Inspected Barrels


    Military specifications require that barrels undergo a HPT (High-Pressure Test) load as a part of quality assurance procedures. Commonly referred to as a proof load, the M197 HPT is rated for 70,000 psi. BCM barrels are proof loaded and then MPI (Magnetic Particle Inspected) to detect any possible flaws in the barrels surface. The barrels are MP inspected with both circular and longitudinal magnetic fields per ASTME1444-01 (current Mil-Spec) to assure a high quality finished product. All BCM barrels are marked HP MP as our proof load marking.
    The term milspec is meaningless. Go to any gun show and everything you see will be milspec. It’s become to broadly used to sell stuff from people that don’t understand what it means to people who don’t understand what it means.

    I also went to the Daniel Defense sight and notice that they make no claim to HP test, just MPI.

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