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Thread: MR556A1 barrel vs 416

  1. #11
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    And Were OFF.....NEXT

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    Quote Originally Posted by InshallahTech View Post
    This also proves effectively once and for all that cutting any 416 or MR barrel from 16 to 14.5 or to 10.4 will have no effect on the taper of the bore at the muzzle.
    I measured negligible, but still measurable velocity loss (0.29-0.64%) between two 14.5" MR223 barrels (with close round count). One was cut from 16.5" barrel, second ("faster" one) was factory 14.5" barrel.

    All data is here: Montrala: Cutting HK MR223/MR556 barrel - good, bad or ugly?
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  3. #13
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    How thick is Chrome Plating on Barrels?

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    Quote Originally Posted by NoScoE30 View Post
    Lets start with my sample set.

    20 "turner" barrels

    10 "turner" barrel ends (probably used to be attached to your turner barrels)

    14 MR556 barrel ends

    1 MR556 upper/barrel


    NONE of them fit a .220"- pin, not with 8.75lbs. I could probably broach the rifling out if I rammed the .220"- pin.

    Its clear that you are an experienced HK armorer, but you should probably check and calibrate all of your inspection equipment. Also, please do not force gauge pins.
    I would say for this discussion, the turner barrels are not applicable.

    Insofar as the Mr barrels go, perhaps I just have a crap one... That shoots incredibly well. Yet also starts to possibly solidify my cynical side that thinks perhaps that HK sends their rejected 416 barrels to the MR line before they are chrome lined.

    In case you missed it, I did NOT use 8.75lbs force on the pins. I gave that info merely as an example.

    Gauges need some "pressure", not force. Unless as many variables are removed without causing damage, you will not get a good reading. The firing pin protrusion gauging for an M240 series mg is a prime example. Rivet movement cannot be seen most of the time on the bolt until the fp gauge is used and pressed firmly in to remove all movement of the components.

    Any gauging that is variable isn't gauging at all, it's guessing. Yet i do agree that gauges should not be "forced" because it can cause damage to the gauges and/or weapon.

    Lastly, the first thing I did when you made your first comment was cal my gauges and re-gauge just to make sure my ducks were in a row..
    Last edited by InshallahTech; 11-01-2017 at 06:40 AM.

  6. #15
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    Quote Originally Posted by Montrala View Post
    I measured negligible, but still measurable velocity loss (0.29-0.64%) between two 14.5" MR223 barrels (with close round count). One was cut from 16.5" barrel, second ("faster" one) was factory 14.5" barrel.

    All data is here: Montrala: Cutting HK MR223/MR556 barrel - good, bad or ugly?
    Montrala, Yours is a sample size of exactly one each.

    I'd have trouble accepting that as solid fact with even a sample size of 10 or 20. A hundred each maybe.

    Barrels are like snow flakes, each one is special. No two barrels will perform the same even if they rolled off the production line one right after the other.

    Also think about the physics involved. What sense would it make to have bore tapering that goes past the gas port? That would cause inconsistent pressure at the port, cause pre-mature port wear, and inconsistent function of the weapon.

    That being said, I look at my own examples and understand that my readings are different from two different barrels of exact same lineage and NoScoE30 made a good catch on that one.

    Now we have my second MR barrel and his barrels that gauge the same and differently from my first. The 416 barrel I have here will be considered moot for the remainder of this discussion.

    That being said, I think the big variable not being considered is that my MR barrel that gauges out to .220 has been nitrided.

    Perhaps this is a side effect of the nitriding? Perhaps the process causes ID to expand due to the factors involved and this is a possible drawback to the process. But even then i'm not so sure it's necessarily a drawback as this barrel was a sub MOA barrel after nitriding and before it was cut back to 10.5.

    I'm this ---> <---- close to going to Amazon and purchasing enough pin gauges to make a set extending from .217 to .224 stepped up in thousandths and having it passed around to well standing HKPro members with both non nitrided and nitrided barrels to get a better sample size by comparison.

    I also still have my nitrided MR barrel stub from the cut down and will drop the gauges through it in a few days after I find it.

  7. #16
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    One thing that is clear is the MR556 is not simply lacking the chrome. With the bore sizes being the same as the 416, adding any chrome to an MR556 barrel will take it out of tolerance.

    Make sure you know the difference between pin gauge classes, and + and - sizes if you are ordering pin gauges.

  8. #17
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    Quote Originally Posted by NoScoE30 View Post
    One thing that is clear is the MR556 is not simply lacking the chrome. With the bore sizes being the same as the 416, adding any chrome to an MR556 barrel will take it out of tolerance.
    I would say that's not exactly clear. The 416 barrel I have here only takes a pin gauge 1 thou smaller then the oversized MR. Since HK is infamous for relying on their barrel steel over chrome lining in the G series guns, they *may* have simply put enough chrome in the 416's to qualify them for US mil service. (keep in mind the 416 barrel has a round count of approx. 5k, which is not enough to wear the chrome full bore that much. This also alleviates my cynical side that says the rejects go to the MR line)

    Another thing to consider is that what we're talking about is the bore diameter of the lands, not the groove. Groove diameter is much more important in many aspects as that is where the actual compression of the bullet takes place. If all the taper is in the lands alone, the lands won't necessarily follow convention that we expect from normal barrels so it's possible that HK's acceptance criteria includes MR barrels with what we would normally consider unacceptable. Remember that the bore taper accepts an M4 bore erosion gauge past the reject line. This means that literally every 416 and MR556 barrel would be rejected according to standard milspec convention as they come brand new from the factory.

    Considering that HK took a very unusual route with bore tapering which is a technique usually reserved to very large bore type guns, it would be safe to assume that there are other conventions that they have eschewed. But it works and that's the beauty of the system.

    I would also ask if all of the barrels you've measured have had full copper removal prior to gauging? It does make a difference.



    Make sure you know the difference between pin gauge classes, and + and - sizes if you are ordering pin gauges.
    Yea, I know the difference. Remember you're not talking to a neophyte.

  9. #18
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    Quote Originally Posted by NoScoE30 View Post
    One thing that is clear is the MR556 is not simply lacking the chrome. With the bore sizes being the same as the 416, adding any chrome to an MR556 barrel will take it out of tolerance.
    I though the bore was etched (made bigger) during the hard chrome lining process?

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    Quote Originally Posted by InshallahTech View Post
    Montrala, Yours is a sample size of exactly one each.
    Remind me how huge is your sample size exactly? 10, 100, 1000?

  11. #20
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    Quote Originally Posted by tlrgsxr View Post
    I though the bore was etched (made bigger) during the hard chrome lining process?
    I imagine the etching process only takes maybe 20 millionths off the surface.

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