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Thread: Action spring pressure measurements.

  1. #81
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    You will notice that I acknowledged that a heavier buffer will fix the issue. Which is what we did temporarily. But the root cause (at least in my experience) was the enlarged port size.

    I may be wrong, about this, but as I understand it the U.S military has been using H2 buffers in their M4's for some time. I know that I saw some in fact with H2's in them.

    So in the cases where I dealt with this, the common link was porn star gas ports+full auto fire. As soon as I received the new barrels and re-barreled the weapons, the issues stopped. I am not an engineer or a rocket scientist, but when I take several carbines with this issue, and I do the exact same thing and I put the same springs and buffers back in the weapon and the only variable that changed was the barrel I have to logically conclude it was the problem.

    If I am wrong so be it.

    Quote Originally Posted by Sparky5019 View Post
    I agree that more gas = more carrier speed and that contributes to the problem. All I'm saying is that, in my mind, one needs to take into account the "bounce" effect even when dropping the BCG by hand (I've done this as well just to see). To me, in SA, gas just can't e the whole answer.

    IG, I respect your experience, service and opinion but I'm kind of with WS6 as to how I understand this one. Now, I also acknowledge that carrier bounce is a multi factorial problem that may be completely solved in 2 totally different ways that share absolutely no connection (1 from the front and 1 from the back). That might just be what we have here; 2 different fixes for the same problem.

    I love how we work out problems and solutions here.



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  2. #82
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    Gunz-
    Im running an LMT Defender. Are there any known problems with the ports in those?
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  3. #83
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    Quote Originally Posted by fixit69 View Post
    My experience with carrier bounce was limited to the st-t2. When using a standard buffer I have had no problems.

    I alway quantified, or justified this by "remove the buffer/find correct buffer weight and problem is suddenly solved" type thinking. When I ran into the problem I did not know what it was. I do know that it would not fire. As I have stated before that is unacceptable. This was about six years ago and caused no end of frustration because I was at a loss. A friend suggested buffer wieght change and wow, suddely the piece of crap I was ready to give up on runs like a raped ape.

    As far as I know their is no quantifiable distance of bolt bounce that will cause FTF. Even if there was you would have to have a slow motion camera to catch it, and something to measure said distance. If all it takes to run properly is a simple buffer change, why not just do that. It will work or I have more work, simple.

    ETA: look above to Heavy Metal's post. He describes the un-camming of the BCG and subsequent movment of the firing pin better than I could.
    How do you know for a fact that the failures were caused by carrier bounce, and that the bounce was not mitigated sufficiently by the buffer?
    The reason I ask is that the 416 also uses a tungsten granulate powder as weight in the buffer, and it does have some carrier bounce as evidenced by the video. Still, never seen or experienced a malfunction that could possibly be caused by carrier bounce.

    That is also why I asked how common the issue is; not bolt bounce itself, but FTF due to excessive bolt bounce.
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  4. #84
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    Now your getting above my pay grade. IG might know this, but I don't.

    My research pointed to this phenomenon. When you have a weapon that functions, then change one variable and it doesn't function, you have a very small window of the answer to the problem. Especially when you change said variable back and all is well again. But, finding the problem doesn't alway give you the answer.

    I've never had any time with the 416 so I can't comment on that.

    As to how common voice occurs, I can only say that in roughly 15 years if ownership and messing with them a lot the past 8 years, this episode with the st-t2 is the only time I have seen it personally.
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  5. #85
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    Hopefully I can shed some light on this observation.

    There are several interrelated things going on.

    1)

    Bolt bounce is related to energy.

    Specifically the kinetic energy of the BCG, mass times velocity squared.

    So the faster the BCG slams home, the higher the bounce energy and the more it wants to bounce back.


    2)

    When the buffer bottoms out in the receiver extension on the recoil stroke, the plastic "bumper" on the tail of the buffer is doing the work.

    This bumper returns some of the energy from the impact.

    It probably returns 30-50% of the rearward energy, and this results in some forward velocity of the BCG.

    The action spring adds its energy and accelerates the BCG to it's peak speed.

    3)

    A large gas port will send the BCG backward with more velocity/energy than the action spring can store.

    This causes the buffer to impact the RE, with the extra energy that was not stored in the spring.

    This extra impact sends the BCG goes forward with extra velocity and this results in greater amount of bolt/carrier bounce.


    In Neanderthal:
    A big gas port makes the action slam harder on both ends of the stroke.

    Quote Originally Posted by Iraqgunz View Post
    Well unless I have been lied to, the issue almost always occurs with full auto and usually with crappy barrels. The larger the port, the more gas flow. More gas equals more carrier speed. Now add in full auto where the cyclic rate is increased and the issue becomes apparent.

    The only time I know of this happening is with shitty ass barrels with Kacey Jordan gas ports and incorrect buffers. Or barrels that have experienced gas port erosion= larger than they started out.

    I could be completely wrong here, but when it happened to our Shitmasters and I re-barreled them it disappeared.
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  6. #86
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    Quote Originally Posted by Clint View Post
    Hopefully I can shed some light on this observation.

    There are several interrelated things going on.

    1)

    Bolt bounce is related to energy.

    Specifically the kinetic energy of the BCG, mass times velocity squared.

    So the faster the BCG slams home, the higher the bounce energy and the more it wants to bounce back.


    2)

    When the buffer bottoms out in the receiver extension on the recoil stroke, the plastic "bumper" on the tail of the buffer is doing the work.

    This bumper returns some of the energy from the impact.

    It probably returns 30-50% of the rearward energy, and this results in some forward velocity of the BCG.

    The action spring adds its energy and accelerates the BCG to it's peak speed.

    3)

    A large gas port will send the BCG backward with more velocity/energy than the action spring can store.

    This causes the buffer to impact the RE, with the extra energy that was not stored in the spring.

    This extra impact sends the BCG goes forward with extra velocity and this results in greater amount of bolt/carrier bounce.


    In Neanderthal:
    A big gas port makes the action slam harder on both ends of the stroke.
    Wouldn't the dead blow action of the weights in the buffer damp it's return off the buffer tube, or does the elastic bumper overpower this effect?

  7. #87
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    Quote Originally Posted by WS6 View Post
    Wouldn't the dead blow action of the weights in the buffer damp it's return off the buffer tube, or does the elastic bumper overpower this effect?
    Exactly...

    Lacking some hard data, I'm thinking Clint might be spitballing. 30-50% seems awfully high.

  8. #88
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    It may be spitballing, but the "deadblow" effect can only absorb so much of the energy before it's overcome. I can whack a deadblow hammer hard enough against a cement floor that it will rebound. Not nearly as much as a forged steel hammer, but it is noticeable. Like hitting a bump bigger than the shock absorbers in your car can handle.

    Also, when the carrier closes, it's not the buffer that stops forward motion, it's the carrier hitting the barrel extension- steel on steel- like a hammer against a steel plate. It will be a sharp rap and the buffer won't have anything to say about it until after the shock reflects back into the carrier. If there was a buffer between the carrier and the barrel extension, it would be different.

    Carrier speed of an over-gassed AR can be controlled with a heavier buffer and changing the spring rate but increased mass at the same velocity results in more momentum. Momentum is energy which means the carrier is hitting the barrel extension harder, increasing the chance of barrel bounce.

    IG's analysis is right on the money
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  9. #89
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    No experience with it. I would guess that LMT probably is smart enough to know the correct size. And unless you are running it with an auto lower it will be moot anyways.

    Quote Originally Posted by Straight Shooter View Post
    Gunz-
    Im running an LMT Defender. Are there any known problems with the ports in those?



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  10. #90
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    Quote Originally Posted by MistWolf View Post
    It may be spitballing...
    I was only addressing the 30-50% energy return.

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