Barrel Movement - Page 3


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Old 01-11-2014, 10:15 PM   #21
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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.
i seriously doubt you are bending the barrel of a rifle. you are probably seeing the stock deflection not the barrel moving. you do realize that barrels are heat treated so they are stiff.


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Old 01-11-2014, 10:23 PM   #22
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Would it be correct to think a bull/heavy barrel is less receptive to vibration/harmonics/whip than a standard barrel?

Would it be correct to think that a 30-06 round ,would cause more whip/vibration/harmonics than .22 cal due to heavier bullet, more pressures , more heat ,in barrel.

Therefore a Bull barrel on .22 rifle would nearly eliminate all the vib/har/whip ?

Jim



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Old 01-11-2014, 10:25 PM   #23
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Yes, that is correct, the way you laid it out.

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Old 01-11-2014, 10:37 PM   #24
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Would it be correct to think a bull/heavy barrel is less receptive to vibration/harmonics/whip than a standard barrel?

Would it be correct to think that a 30-06 round ,would cause more whip/vibration/harmonics than .22 cal due to heavier bullet, more pressures , more heat ,in barrel.

Therefore a Bull barrel on .22 rifle would nearly eliminate all the vib/har/whip ?

Jim
heat causes higher fluctuations in barrel harmonics. a larger barrel diameter can take more shots before heat becomes as noticeable in sporter type barrel. for example; it may take 3-5 shots before group sizes open up in a sporter barrel if shot in rapid fashion, whereas it may take 10-15, before group sizes open up in a varmint or target barreled rifle.

these barrel harmonics are nothing that can be seen with the naked eye as they happen too quickly and of such a minor movement that without special photography, it can't be seen. these harmonics happen to every barrel when it's fired. it even happens to very high precision shooting rifles that shoot one hole groups at very long distances. so this movement IMO plays a very small role in the overall accuracy of a rifle if one learns that it exists and tunes for it. i think heat is a bigger factor in opening up group sizes.
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Old 01-12-2014, 01:00 AM   #25
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heat causes higher fluctuations in barrel harmonics. a larger barrel diameter can take more shots before heat becomes as noticeable in sporter type barrel. for example; it may take 3-5 shots before group sizes open up in a sporter barrel if shot in rapid fashion, whereas it may take 10-15, before group sizes open up in a varmint or target barreled rifle.

these barrel harmonics are nothing that can be seen with the naked eye as they happen too quickly and of such a minor movement that without special photography, it can't be seen. these harmonics happen to every barrel when it's fired. it even happens to very high precision shooting rifles that shoot one hole groups at very long distances. so this movement IMO plays a very small role in the overall accuracy of a rifle if one learns that it exists and tunes for it. i think heat is a bigger factor in opening up group sizes.
Very true heating the barrel causes slight changes in the cross section of a barrel and this causes the change in barrel harmonics. The individual harmonics are too small to see but the gesalt total result can be seen. Heat is the cause but changing barrel harmonics are the mechanism that causes groups to open up. Try heating a tuning fork and it will change pitch.

Simple experiment take any free floated, accurate rifle. Shoot a group as a base. Then put a temporary foam and duct tape pressure pad under the barrel. Shoot group and move the pad forward after each group. Simple example of changing barrel harmonics and group size. Plus you might find the accuracy sweet spot for your rifle...
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Old 01-12-2014, 01:22 AM   #26
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Harmonics are why a barrel is rifled at a certain twist and crowned at a certain length for s certain weight of bullet at a certain velocity. The idea is for the bullet to exit the barrel at the precise moment it is not vibrating.

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Old 01-12-2014, 01:32 AM   #27
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Harmonics are why a barrel is rifled at a certain twist and crowned at a certain length for s certain weight of bullet at a certain velocity. The idea is for the bullet to exit the barrel at the precise moment it is not vibrating.
True, certain combinations of rifle twist and barrel length produce " sweet spots" for a given weight/ velocity of ammo. This is where the barrel is at a full harmonic, not because its dead still. The barrel is still a wave down its length but the crown of the barrel is at a node of the wave, and moving the least, that's what a sweet spot is.

The barrel is always vibrating as the bullet is passing down it. And the act of the bullet going down the bore changes the "tune" of the barrel. So the idea isn't "not vibrating" but always at the "same point" in the vibration every time. This gives the tightest groups.

The engineering model of all the forces acting on a barrel is a gold plated bear. Its easiest to picture a simple tube spring...

The vibration damps out quickly as the bullet leaves the muzzle. And the motion is just a few thousandths of an inch. Much less than most of us twitch when we shoot. No doubt this is a minor concern for most shooters. Just us OCD high accuracy guys stress about it...
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Old 01-12-2014, 01:51 AM   #28
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Harmonics are why a barrel is rifled at a certain twist and crowned at a certain length for s certain weight of bullet at a certain velocity. The idea is for the bullet to exit the barrel at the precise moment it is not vibrating.
a barrel is rifled at a certain twist ratio to stabilize a particular range of bullet weights. hence the reason you can rebarrel a rifle in a particular caliber in the twist ratio to work with a certain bullet weight to gain accuracy. plus there in not any concrete evidence that supports barrel length is the only proponent of accuracy. adding length does help add velocity by completing the burn of the powdr inside the barrel. but there have been tests done that show a shorter barreled rifle to be just as accurate as the same rifle with a longer barrel. there is even some belief that a shorter barreled rifle can be more accurate because it's stiffer and has less barrel harmonics than that of the same rifle with a longer barrel, of the same diameter.
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Old 01-12-2014, 02:02 AM   #29
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I've seen some of those studies on short stiff barrel accuracy and the jury is still out. It always seems that the best accuracy for a given bullet/velocity is at the same barrel lengths. Personally I think the wave/ node model is a little closer. Cut the barrel length to corospond to ANY node of the wave and the accuracy will be good. A complex wave with lots of nodes works well in a variety of lengths. A long simple wave might only shoot well in a few lengths farther apart.

This is only if the length is enough to burn the powder charge. And isn't so long as to let the bullet start to loose velocity due to drag. Damn, keeps dropping into sweet spots!

I can't help but notice all of us long range guys shoot the longest barrels we can get. Some of that is pure longer sight radius. But now I start to wonder....

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Old 01-12-2014, 02:09 AM   #30
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I've seen some of those studies on short barrel accuracy and the jury is still out. It always seems that the best accuracy for a given bullet/velocity is at the same barrel lengths. Personally I think the wave/ node model is a little closer. Cut the barrel length to corospond to ANY node of the wave and the accuracy will be good.

This is only if the length is enough to burn the powder charge. And isn't so long as to let the bullet start to loose velocity. Damn, keeps dropping into sweet spots!
just a lot of variable to digest to see what is most accurate. barrel diameter, length, fluting, rifling and other factors. then we could throw in whether a stainless barrel is more accurate than a chrome moly barrel!

i have even read stories in the past where a rifle builder trying to get every little measure of accuracy from a barrel would have removed half an inch to an inch and effectively decreased group sizes by a decent margin.

i believe there is as much artwork as there is science in building an accurate rifle.


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