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Thread: Bolt life question.

  1. #61
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    Quote Originally Posted by sinlessorrow View Post
    that is exactly why the BCG PiP was dropped, they had to work with the existing barrel extension, and they had to be able to use the standard cam pins.

    with those set parameters nothing offered even a 25% increase but all cost nearly double.
    As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.


    Time will tell though.....




    C4

  2. #62
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    I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
    Montrala

    I'm sponsored competition shooter representing Heckler&Koch, Kahles, Hornady and Typhoon Defence brands in Poland, so I can be biased

    http://montrala.blogspot.com

  3. #63
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    Quote Originally Posted by montrala View Post
    I would add, that HK bolt gets also less thermal fatigue (heating to high temp and then cooling) than DI bolt - if used as directed (eg. as assault rifle or automatic rifle, not MG). In HK's that are abused by FA fire, when used in role of suppressive weapon (constant 'break contact' drills - dump mag(s), move, dump, move, da capo al fine), there are reports of bolt failure after about 10-15K rounds of such use.

    Anyway, this shows that when increased thermal fatigue comes in place, there is no easy "workaround". Piston gun bolt usually gets less thermal fatigue, but even then, users are able to "kill them" by enough abuse.

    It would be interesting to know what practical rpm ratio was used for cited research. There is mention 1800 rounds with cleaning every 300 rounds, but it is quite different thermal load when shooting one mag at 10rpm, then taking a break for 5 mins for next mag or shooting 10 mags in a row, even with same 10rpm pace (not to mention 20 or 30 rpm).

    Someone did a heat comparison on this website and bolt had a difference of 40* certainly not enough to cause damage according to Constructor which seems to require around 900*.


    Quote Originally Posted by C4IGrant View Post
    As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.


    Time will tell though.....




    C4
    Thats kind of how I feel about it too, Kevin B mentioned something similar and thats why they chose to focus on the PiP and opted out of the IC


    Quote Originally Posted by C4IGrant View Post
    There is a .Mil 416 user on here that has told me many times that they typically break bolts on the 416 around 12k.



    C4
    Excellen info, thanks for adding that.

    To Sinister great post thats interesting about the barrel change every 3,000. Also adds a number to the bolt discussion beyond what I had.

    I can certainly see an increase in material adding to strength. Will be interested to see the number diff between the two bolts
    Last edited by sinlessorrow; 06-06-12 at 13:13.

  4. #64
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    Quote Originally Posted by montrala View Post
    I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
    That is our max size at the cam pin area also but because the carriers aren't always perfect(try to keep a bolt tail hole in the center when using a 5" long drill bit) we try to keep them at .526 for a little wiggle room.
    AR15performance
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  5. #65
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    Quote Originally Posted by montrala View Post
    I do not have M4 bolt at hand, but HK bolt is 0.528" (on my crappy caliper) diameter at cam pin hole.
    Ill measure m bolt tonight with mt calipers

  6. #66
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    Finally fount the micrometer.

    M4 bolt = .512 OD at the cam pin
    and .101 wall thickness at cam pin

    HK bolt = .53 OD at the cam pin
    and 1.11 wall thickness at cam pin.

    M4 bolt = .101 lug thickness

    HK bolt = .101 lug thickness.

    Obviously, my eyes decieved me regarding lug thickness, but I was correct about the bolt diameter difference.

    Like I said earlier, an M4 bolt fits freely into the MR556 carrier even with gas rings, but the HK bolt will only fit part way into an M4 carrier. It stops just before the cam pin hole is fully inside the carrier. This is caused by the piston ring bore on the inside of the carrier itself.

    An examination of the HK bolt and the M4 bolt (noveske) show that the bolt lug joints (angles at the rear of the lugs where they transition from the rear of the lug into the rest of the bolt, a 90 degree transition)) are more radiused on the HK bolt, allowing for better fatigue resistance. Matter of fact, every angle and joint on the HK bolt is radiused, and to a better extent then anything on the DI bolt. Any metal worker will tell you that sharp angles create weak points in your material, and HK seems to have made every attempt to minimise this issue.


    Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:

    At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.

    What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.

    Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.

    At this point, I can't find a single negative aspect of nitriding gun parts.

    Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.

    If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
    Last edited by GrumpyM4; 06-06-12 at 18:11. Reason: Further observations
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  7. #67
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    Quote Originally Posted by jwperry View Post
    Heat transfer.
    Quote Originally Posted by Heavy Metal View Post
    Why? The BCG gets nowhere near hot enough to affect the temper of the steel. A couple hundred degrees at best.
    Yeah, I thought the heat transfer concern was thoroughly debunked with the use of thermal cameras and other technology...

    It sounds like there are many variables when talking about bolt life:
    manufacturer
    type of steel used
    QC of manufacturer
    type of gas system (carbine/middy/rifle)
    full auto fire
    suppressed fire
    lack of lubrication

    Can there really be a definitive answer to the bolt life question?

  8. #68
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    Quote Originally Posted by GrumpyM4 View Post
    Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:

    At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.

    What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.

    Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.

    At this point, I can't find a single negative aspect of nitriding gun parts.

    Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.

    If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
    Simplicity is always key IMHO.
    Ive been very interested in QPQ since reading the nitriding thread. It seems to be a big improvement to metallurgy and firearms overall. Thinking about it now, from this post, if the numbers check out (added cost vs. added performance), it could be a viable direction, not to mention an easier transition for the military.

  9. #69
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    Quote Originally Posted by Col_Crocs View Post
    Simplicity is always key IMHO.
    Ive been very interested in QPQ since reading the nitriding thread. It seems to be a big improvement to metallurgy and firearms overall. Thinking about it now, from this post, if the numbers check out (added cost vs. added performance), it could be a viable direction, not to mention an easier transition for the military.
    the issue is no one seemed to enter a Nitrided BCG, they were either phosphated or NiB which I have never been impressed with

  10. #70
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    What I would like to see is for Colt to be able to embrace some of the new(er) developments and products on the market to help improve the M4.

    Quote Originally Posted by C4IGrant View Post
    As we all know, Army is going through their down selection process for an M4 replacement. My thought is that once they have a winner, they will then test it head to head with the M4 and they will find out that it is NOT 25% better and cost is DOUBLE and drop the piston gun and stick with the M4.


    Time will tell though.....




    C4



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