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Thread: AR15 Performance Super Bolt

  1. #41
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    AAC bolts are C158.

    I looked into making the body diameter larger. I did not pull our drawings, but I measured a bolt - and the bearing surface was only 0.018 larger diam than the cam pin area - so that is just 0.009 per side. I don't think that leaves much room to make it larger - and I like the space for goop to go somewhere.

  2. #42
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    The difference between good and less good bolts are:

    Good use C158, lesser uses 9310, and lesser still uses 8620.

    Good has a thorough shot peen, to ASTM B851 specs. Less good uses shot peen that does not meet B851, and bad would be skipping shot peen. It is very important.

    Good has a nice surface finish and was vibratory tumbled. Bad has areas where cracks can form.

    Good has all specs dimensionally correct to the drawing. Bad has dimensions out of spec.

    The problem is - people don't inspect their bolts to see if they are dimensionally in spec - so they are happy just to know it is MPI, which seems to be associated with being good. It is treated like a stamp of quality, but is by far the least important thing.

    If 1 or 2 in a million bolts fails MPI, but 100,000 in a million fail a dimensional check - where should you spend your QC budget for screening parts?

    By the way, even the bolt that does "fail" MPI is probably still a bolt with thousands of rounds of life left in it as it just has a microcrack on it that all AR bolts have after 3,000 to 5,000 rounds.

    What I care about, aside from the obvious like using C158 and S2 extractors and extractor pins (which by the way - many use S7 without you knowing), is the detailed shot peening work.

  3. #43
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    Quote Originally Posted by rsilvers View Post
    If 1 or 2 in a million bolts fails MPI, but 100,000 in a million fail a dimensional check - where should you spend your QC budget for screening parts?
    But as we discussed before (to which you never provided an answer to) was that we don't have that info available to us in order to make the right decision. Is it 1/1,000,000? Is it more, is it less? I was provided a number by someone who is someone that is certainly not 1/1,000,000.

  4. #44
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    I know - that is a problem that there is no public info on the failure rates. But it is close to 1 in a million.

    That is to be expected, right? If a typical bolt does not form a micro-crack until 5000 rounds, what percentage of bolts would be expected to form a micro-crack after 1 proof round? Essentially none.

    It was a good test 50 years ago, as lots of people did not believe the aluminum and plastic rifle was durable.

    Here is something else to think about...

    If you took a million bolts that were never MPIed...

    and you took a million bolts that were MPIed and passed...

    And you put these two million bolts into combat...

    Would more bolts from the non-MPIed group fail before the bolts from the MPIed group?

    In other words, would you statistically be able to tell which group was which based purely on the failure rate in the field?

    Of course not.

  5. #45
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    Quote Originally Posted by seabass03 View Post
    what are the list of companies that sell carpenter bolts?

    BCM and Colt for sure
    LMT and DD?
    PSA advertises their bolts as being Carpenter 158 and shot peened, HPT and MPI.

  6. #46
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    Question for people who are more comfortable with MPIed bolts...

    If you have 3000 rounds on your rifle, your bolt will probably fail MPI now. Under your own logic, are you not then compelled to discard your bolt? Why not get it re-MPIed every 1000 rounds and discard it upon failure?

  7. #47
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    Quote Originally Posted by Bad Hammer View Post
    PSA advertises their bolts as being Carpenter 158 and shot peened, HPT and MPI.
    Ask them, Colt, DD, LMT, and BCM if their extractor and pin are made from S2 or S7. I actually don't know the answer, except Colt will be S2. For a smaller company, S2 is often unobtanium but 30% stronger. Rob_S should add S2/S7 to the chart.
    Last edited by rsilvers; 12-03-11 at 22:32.

  8. #48
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    Quote Originally Posted by rsilvers View Post
    I know - that is a problem that there is no public info on the failure rates. But it is close to 1 in a million.
    As I said before, if it is that low I would take the non-HPT bolt any day of the week, in bulk, and have them x-ray'd through work (assuming free).

  9. #49
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    Quote Originally Posted by rsilvers View Post

    If you have 3000 rounds on your rifle, your bolt will probably fail MPI now.
    I would hope not as the A2 spec calls for passing the MPI after the 6,000 round endurance test.
    Last edited by Tweak; 12-04-11 at 02:54.

  10. #50
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    Quote Originally Posted by seabass03 View Post
    what are the list of companies that sell carpenter bolts?

    BCM and Colt for sure
    LMT and DD?
    Rainier as well.

    http://www.rainierarms.com/?page=sho...roduct_id=2633

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