Barrel Movement

Discussion in 'General Rifle Discussion' started by dexntex, Jan 11, 2014.

  1. dexntex

    dexntex New Member

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    I've recently observed that if I push and pull on the end of the barrel of a heavy-barreled, long-range Savage 112 BVSS, I can see the free-floating barrel move relative to the stock. The action is torqued to 50 inch-pound in its pillar-bedded laminated stock. I thought everything would be rigid and not move. I was surprised thought maybe there was something wrong with the rifle. Then, I did the same thing to a Remington 700 Sendero. On the Remington, the action is torqued to 45 inch-pounds in an HS Precision synthetic stock with a full-length aluminum bedding block. How could there be movement. Is this normal?
     
  2. JonM

    JonM Moderator

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    Its normal.don't try to "fix" it.

    All barrels vibrate as the bullet travels down the tube the reason for free floating is so the stock does not interfere with that vibration giving more consistent shot groups.
     

  3. TLuker

    TLuker New Member

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    I've always known that the barrel vibrates when fired but I would have never guessed you see the movement just by applying pressure with your hands. Interesting! :)
     
  4. JonM

    JonM Moderator

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    yup barrels bend but what the op is seeing is most likely the stock itself bending making it look like the barrel is. take the stock off and try to do the same thing i doubt your going to see any perceptable movement.
     
  5. Mercator

    Mercator Active Member

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    A forend play around the barrel is normal for a free floating barrel, but not for a bedded one. Bedded means attached. As long as your barrels are spec'd to free float, you are good.
     
  6. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    that movement the stock makes bothers some people. myself included and it's an easy fix if it does bother you. a steel rod and some epoxy will make the fore end stiffer and not flex as much.
     
  7. Mercator

    Mercator Active Member

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    Just wanted to add, a free floated barrel by itself is not the cat's meow of rifle construction. It is often advertised as a big deal, but actually it is a way to sidestep the stock fitting procedures. A good bedding whenre the barrel and the stock oscillate in harmony is more expensive.
     
  8. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    please explain the barrel and the stock oscillating in harmony. my experiance has been to lock the reciever and the stock into one cohesive unit and to allow the barrel to be free floated so it not affected by pressure from the stock.
     
  9. Mercator

    Mercator Active Member

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    The stock acts as a dampener. There will still be some oscillation, but much less than in a regular size free floating barrel. The heavier the barrel relative to the projectile, the less it benefits from a bedding. A lighter, thinner barrel may experience a significant whip affecting its mechanical accuracy.
     
  10. dteed4094

    dteed4094 New Member

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    I have always thought and told; any movement between the stock and the action is detrimental to consistency hence accuracy. I understand the harmonics but the more you reduce barrel whip, the more consistent your groups will be.
     
  11. mountainman13

    mountainman13 New Member

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    Wood and steel will never be affected the same way by a shock.

    better judged by twelve than carried by six.
     
  12. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    all barrels when fired have harmonics. the rifling is the key to a barrels accuracy. the rifling will affect the barrel harmonics when a round is fired. the barrel when shot heats up and heat will affect the barrel harmonics as well.

    with the stock and action you are looking for a solid foundation. if there is movement between the two, then accuracy will suffer. accuracy comes from consistency in all the variables when shooting. everything with the rifle is consistent. everything about the shooter is consistent and everything about the ammo is consistent.
     
  13. JonM

    JonM Moderator

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    the amount of movement or barrel whip doesnt matter if it does it the exact same way everytime.
     
  14. Mercator

    Mercator Active Member

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    That's correct, that's what a good bedding job does - improve the mechanical accuracy by dampening the whip. Good precise bedding is better than no bedding (free float), but no bedding is better than poor bedding (random points of barrel/stock contact).

    With a genuinely free floating barrel AT LEAST the stock does not make things worse by touching the barrel here and there. If it does, every shot will cause variable harmonics ---> larger groups.
     
  15. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    i have even read in the past, that different weight bullets and different powder charges change the barrel harmonics to some degree, hence why some loads are more accurate than others.
     
  16. JonM

    JonM Moderator

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    thats correct.

    not all barrel cartridge combinations do well with bedding bedding a rifle stock can be a negative depending on materials. a bedded wood stock will change properties with humidity and temperature while bedding a synthic has typically good results if done correctly.

    what you bed isnt the barrel but the reciever stiffening it and damping vibrations.

    a poorly floated barrel that contacts the stock on vibration is worse than clamping the stock in a barrel band.

    it all boils down to materials and who is doing the work. most stocks that come with guns off the shelf are pretty crappy which is why there is a huge aftermarket stock selection of manufacturers...
     
  17. Axxe55

    Axxe55 The Apocalypse Is Coming.....

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    and every rifle is different as well. some even like a little pressure pad at the fore end to gain accuracy.

    personally i bed my rifles with about the first 3-4" of the barrel with the action and free float the remaining portion of the barrel with good results. one Remington M700 in 30-06 i did, went from about 3/4" groups down to just over 1/4" groups after bedding the stock this way.
     
  18. dexntex

    dexntex New Member

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    Yes, it surprised me too. I also knew that barrels bend and vibrate when firing but didn't know you can cause it to happen and see deflection by pushing up and down or sideways with your hand. Like I said, the Sendero barreled action is solidly planted in a full length aluminum bedding block and still you can see the relative motion of the barrel with the stock. And after 550+ plus rounds through the Sendero, I know the rifle is accurate so I guess the motion is not a problem.
     
  19. dwmiller

    dwmiller Well-Known Member

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    Easiest way to picture it is to think of the barrel as a spring. It will move in three directions when a shock load (bullet fired) is applied and the oscellate as is goes back to its resting state.

    It is compressing a small amount from the bullet being accelerated. This is very small +-0.0001 or less since steel is very strong in compression.

    It is torqued around the surface of the barrel by the mechanical action of the rifling acting on the accelerating bullet. Think of twisting both ends opposite dirrections. Again very small, steel tubes are a strong form to resist torque.

    Finally the barrel will whip up and down, or left to right. This is caused by harmonics of the above forces, but is the most easily seen since the long thin tube bends easiest in this direction. Sometimes as much as +-0.002 on magnum rifles.

    Free floating the barrel and bedding the action solid is the best way we have found to get "consistent" barrel movement and shot placement. The barrel springs the same way each time as long as the shock load is the same. This gets the bullet to strike the same area each time... ;)
     
    Last edited: Jan 11, 2014
  20. Mercator

    Mercator Active Member

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    Your hand does not flex the barrel like a tuning fork. It only shifts the stock relative to the barreled action (or you could say it vice versa) This is a mere free play. It does not correspond to the barrel oscillations caused by firing a projectile through it. Those are two different things. They may well coexist, but they are not the same.

    It is true that the ballistics of a given projectile and the physical characteristics of the barrel are a unique combination that result in more or less "barrel whip". The barrel, as any system, will oscillate with a greater amplitude at some frequencies than the others. That is why a given firearm is known to "like" some ammo and "dislike" the other. No theory can fully predict the accuracy of your rifle. Certainly not the "free play" in the stock. It may not "feel right" but is a poor predictor of accuracy in itself.