I would like to know how they came to that conclusion first. Just because Colt does it is not the way to go, not ignoring the fact that they have making AR's/M4's down pat.
Plus I would not be able to enjoy my N4's as much. :p
It's just an example of if a track record should be enough. If they can't make bolts that pass HPT/MPI after all these years I would say there is a design flaw.
I've always wondered how much the pressure increase when the 5.56 ammo was developed plays in the service life of the M16 bolt?
Interesting thread.
One observation: the more things change, the more they stay the same.
I have a book from 1834 about firearms manufacturing/metallurgy and testing and safety for the British Army. One thing that was common back then was for manufacturers to make guns of unsafe quality that demonstrated alarming numbers of catastrophic failures to the point that guns made in Africa in particular were very unsafe.
The author of the book advocated laws that required government proof-testing of all English-made weapons for the safety of the end-user, and also for the benefit of the British military. Now these were old black-powder muskets, not modern ARs, but still very interesting that such issues (in a mcaro, not a micro sense) are well over 150 years old.
I don't think it's outdated.
The purpose of the chart was to determine why product X was better than product Y, and the end result was that it was because product X had certain measures performed that made quality control more strict than product Y.
HPT/MPI was one of those things, and the ONLY ONLY ONLY reason I give KAC the pass on not performing HPT was because they've never had a reported case of a broken E3 bolt.
I believe there are exceptions to every rule, but IMO, if I were launching an AR MFG tomorrow, I would HPT/MPI everything that leaves my doors.
I believe it is necessary.
Including your triggers?
I think the thing to remember is the parts that are MPI'd are ones that could potentially cause harmful failures. I am pretty sure that broken triggers do not cause harm,
and bringing up triggers makes me think, hmmm well they do not have near the potential for the high pressures that the barrel and bolt have.
''They were all proof testing in accordance with various laws.'' its a government run system without a dark evil plot to ban/control weapons -just a proof set for Q/C if it fails this its junked and all is stopped ! was it too hard or too soft or alloy was wrong etc .. its about Q/C i am in favor of a national proof house .. i can hear some decry this as gun control .... but who will can clean up the mess of crappy made weapons as well like dirty companies like Hessie !!!it's Q/C!!!
I am glad that we’re having the discussion in an adult manner; I’ve called into question the TDP thumping specifically over HPT/MPI and caught a little bit flack over it before. I’ll preface this by saying that I work in QA, as a data analyst dealing specifically with nonconforming product at an API Q1/ISO 9001:2008 facility; I’m also a quality management system auditor and ASQ member pending certification next month. We’re also really big into Crosby Quality and being zero defect capable. If you’re familiar with Phillip Crosby you’ll recognize this gem: The definition of quality is conformance to requirements: not “goodness” or “elegance”.
I think that HPT/MPI testing on every bolt and barrel is overkill, and in all likelihood a carryover from 50 years ago that’s probably no longer necessary today. This isn’t an all or nothing proposition, batch testing is probably a “better” idea from a manufacturing standpoint but as long as the TDP calls for testing each one (and it’s really the only published spec for building a “mil spec” carbine) most people will have a hard time accepting anything else (notice I said “else”, not “less”). The perception is that anything that does not adhere to the TDP is suspect even though we know there are weaknesses in the legacy system even though a fair number of them have been addressed through aftermarket sources that are nowhere close to the TDP. I think it's high time people get over the TDP thumping as if it was the only way to build a decent rifle.
rsilvers points on parts being dimensionally out of spec does occur to me as being the root cause for brands held in complete ill repute on this site (they fail with a small round count), versus the metallurgical problems examined by the HPT/MPI process that won't manifest for thousands of rounds in most cases.
Even more so that part dimensions at extremes (or outside) design tolerances probably do more to exacerbate metallurgical problems as much as the firing schedule that rifle sees.
Going of the assumption that most 'bubba rifles' won't see more than 100 rounds a season, I think there might really be a case for prioritizing other aspects of the spec before HPT/MPI...
However, given the proliferation of fantastic options that are made quality AND are HPT/MPI tested (BCM, DD, Colt, LMT, etc.) that are negligibly different in cost, it's silly to buy many of the other brands that don't and roll that difference into their margins.
I do think the rounded edges of the E3 bolt have imbued that design with one less critical failure point (especially since it seems KAC has their metallurgical processing well in hand), and the low failure rate seems to be a result of these two things, along with most E3 bolts being ran on an intermediate gassed system.
My two cents.....
Proof testing is used to create a stress greater than the part should see in service. NDT testing such as MPI should follow, not precede, proof testing to allow stress to open a flaw and make it more obvious.
These production acceptance tests are not done to verify dimensions or design, they are done to find the one in a million flaw. Doing these tests on a sampling basis is assinine. Either do them 100% or don't do them.
Sure, modern steels are more homogeneous and better controlled than in the past, but, nothing wrought by man is perfect.
I have seen aerospace components fail proof and explode.
I have seen aerospace components fail NDT/FPI.
I have seen a forged, rolled thread bolt fail on the first torque cycle. The conclusion from the manufacturers investigation was - no clue - "it was a one in a million failure".
Will a properly made bolt, of the proper material last longer because it was proof and MPI tested than a bolt that was properly made and not tested? You probably could not prove it statistically, without a .gov size database. But, the one that has been tested is less likely to have an unexpected early life failure.
Think one in a million. But, that one instance can ocurr anywhere in the million.
That testing is worth 20 bucks to me. Ymmv.