Barrel Tip Deflection

Discussion in 'ELR, Ballistics & Bullets Board' started by ThunderDownUnder, Jul 6, 2018.

  1. ThunderDownUnder

    ThunderDownUnder

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    If you have trouble sleeping at night then I suggest you read the tech article on using neural networks to calculate barrel tip deflection.

    It seems its possible to calculate the barrel tip deflection caused by the projectile, (moving mass) at least for military purposes and examples used were for 35mm anti-aircraft rounds and barrels.

    I'm sure it could be adapted to be used on target barrels as well.

    It certainly makes clear to me the importance of matched mass and velocity of the projectiles we use!

    Enjoy ;)

    http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-78252016001001968
    https://www.researchgate.net/public..._MM_ANTI-AIRCRAFT_CANNON_BARREL_DURING_FIRING
     
    Last edited: Jul 6, 2018
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  2. damoncali

    damoncali Gold $$ Contributor

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    A bit complex for my taste, but clever.
     
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  3. Eternal Student

    Eternal Student

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    WOW!! I haven't seen that many numbers on a page since college. That just sounds like another name for "barrel whip". Anyone else get that impression?
     
  4. damoncali

    damoncali Gold $$ Contributor

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    That's exactly what it is. It's an attempt at quantifying it, though, which is not easy.
     
  5. JRS

    JRS Gold $$ Contributor

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    Does it really matter? The barrel vibrates much in the same way a guitar string does after the string is plucked/released, or the vibration felt on a bow after the arrow has been released, or the deflection (paradox) of an arrow after it leaves the string.
     
    Last edited: Sep 21, 2018
  6. damoncali

    damoncali Gold $$ Contributor

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    It matters because the force driving the vibration starts immediately as the trigger is pulled, starting with the firing pin impact (which is measurable even without a charge - I think this may be what people are tuning when they start messing around with ignition, at least in part). So the barrel vibrates before the bullet leaves the barrel.
     
  7. JRS

    JRS Gold $$ Contributor

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    Does a tuning fork vibrate as you strike it, or after you remove it from the surface you strike it against?
     
  8. damoncali

    damoncali Gold $$ Contributor

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    When you strike the fork, it bends while still in contact with whatever you hit. The speed with which it starts vibrating depends on the speed of sound in the material, which for steel is extremely fast - about 20,000 feet per second. That's as fast as any deflection can move through a material. Think of it as a wave moving through the material - one end of the fork can't know the other end has been struck until that wave travels across, at the speed of sound in steel.

    So as soon as that wave can propagate through the fork, it is technically vibrating. It's vibrating in a way that's influenced by the fact that there is still contact with the fork, but it's still vibrating. Once you remove the contact, the frequency will change and it will continue to vibrate until it damps out. Notice the "tink" that you hear when you strike the fork. That's the sound generated by the initial vibration. Also notice that it's not the same pitch as the fork's free vibration.

    You have to think of vibration as a dynamic motion rather than a constant sine wave. It's more whip than tuning fork.
     
    Last edited: Sep 21, 2018
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  9. boltfluter

    boltfluter

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    Alex Wheeler is doing some great work in this area. It does make one take a step back, and put on the old thinking cap.Good stuff that we will all benefit from. Thanks Alex. :D:D:cool:

    Paul
     
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  10. JRS

    JRS Gold $$ Contributor

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    Too much overanalyzing taking place.
     
  11. damoncali

    damoncali Gold $$ Contributor

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    I disagree. This is exactly how tuning a rifle works. It's the difference between a 1/2 MOA rifle and a 2 MOA rifle. Understanding this allows us to manipulate it.
     
  12. JRS

    JRS Gold $$ Contributor

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    Personally, I believe most of it comes down to the array of better barrels, bullets, tuners, and the time our better shooters are willing to sacrifice at the bench. Compared to today, the small group record that stood for more than 4 decades was set using much less expensive equipment than we use today, the rifle was not topped off with a 60x $2000.00 scope, the barrel wasn't clocked to a certain position, and B&A triggers didn't exist, and the cartridge was the 222 Remington fired in a button rifled barrel. At some point, hard work and commitment pays off.

    Edit: I'd be willing to bet a dollar to donuts that some of our older shooters could pull out their ancient BR guns and shoot just as small as they do with their current/modern guns. A great deal of what we pay for now is more a matter of luxury and want, rather than necessity. The difference between winning and second place comes down to hard work, commitment and Lady Luck.
     
    Last edited: Sep 21, 2018
  13. mgunderson

    mgunderson sling shooter Gold $$ Contributor

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    The problem gets complex when you talk about the stock and how it interacts with the supports and/or the human body. I also believe Alex is doing some interesting work.

    Varmint Al has some interesting models on his web page that looked at tuners.
     
  14. normmatzen

    normmatzen Gold $$ Contributor

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    Soon as the gun fires, a longitudinal resonance is formed. When the bullet exits the muzzle with respect to the node of this resonance determines the ES of a group. When the bullet tries to fly straight down the barrel, it causes a vertical resonance, or cantilever. This is where you want to tune the barrel so the muzzle points the correct angle to make the bullet hit mid X!

    That's why I test the barrel with round robin 5 shot groups with a series of loads. Best ES as evaluated by Excel and curve fitting tells me the exact load. Then after loading that "perfect" load, I take off the MagnetoSpeed and screw on the tuner weight and do 2-3 shot groups as I adjust the tuner over maybe 0.1" with 1/80" increments.

    And, the correct jump just happens to be at what ever jump I used for the round robin load determination. And, yes, I tried many times to improve with adjusting jump with no success.

    Disclaimer: This can't make a bad barrel shoot great. just allows a good barrel to shoot its best.
    And, Yes, you can replace all this by ladder testing and jump adjusting and get the same result.
     
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  15. dgeesaman

    dgeesaman

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    Both.
     
  16. Ned Ludd

    Ned Ludd Silver $$ Contributor

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    If the last inflection point (node) of barrel vibration is known, the ability to accurately estimate barrel tip deflection would also allow one to make a pretty good estimate of muzzle launch angle. Together, those two values would be pretty useful for predictive in silico load development estimates. Certainly one can always simply load rounds and put holes in paper to achieve the same goal, but I've always believed that predictive tools such as QuickLoad can expedite the process considerably when used correctly.
     
  17. Papa Charlie

    Papa Charlie Silver $$ Contributor

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    While the math is over my head. When you read the conclusion, it is clear that there are three things that create variation and they sum it up with this sentence:

    "The most important parameters affecting a weapon system's dynamics are the projectile-mass, acceleration, and exit velocity."

    and we already know to try and control these through bullet lot numbers and sorting, using the same lot number of powder and accurate measurement of the powder load.
     
    Last edited: Sep 23, 2018

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