Whipping Barrel During Discharge

[hwingo]

Hi Guys,

My question involves a high power rifle barrel whipping when a round is discharged.

1. Does the barrel begin to whip at the moment of powder burn or does it begin to whip *as* the projectile exits the barrel or after the projectile has exited the barrel?

2. If the barrel begins to whip while the projectile is still within the barrel, how does one explain accuracy?

Thanks,

Harold

[danlb]

Whip is after the bullet leaves the barrel in at least the videos that I found.


https://www.youtube.com/watch?v=AqgPu9gSmVc


Dan

[Boostinjdm]

I'm going to say yes to both.

The answer to accuracy is harmonics and the reason tuning is needed for extreme accuracy. You can't eliminate whipping, but you can reduce it and tune for repeatability. Whipping the same every time will net the same results as not whipping at all.

*That's my theory anyway, I'm not an expert.

[mihit]

2) One explains accuracy as the repeated measurement/production of the correct result (bullets in the X ring)

In relation to firearms, that, as said by Boostin, is largely about *repeatability*

1) From the moment of primer strike the bullet exerts torque on the barrel through the rifling. Once the bullet leaves the barrel this torque is no longer applied and the stresses developed are released.

So I reckon it's moving from the go, it just becomes more obvious once the projectile has left the barrel.

[rws]

I'm going to say yes to both.

The answer to accuracy is harmonics and the reason tuning is needed for extreme accuracy. You can't eliminate whipping, but you can reduce it and tune for repeatability. Whipping the same every time will net the same results as not whipping at all.

*That's my theory anyway, I'm not an expert.

This is correct. Vibrations start with the release of the firing pin. The vibrations/harmonics continue until the bullet exits. There are ways to tune these vibrations that will allow the bullet to exit at the same node in the vibration, and accuracy is greatly improved.

[kev74]

2. If the barrel begins to whip while the projectile is still within the barrel, how does one explain accuracy?

As long as it moves the same way each time, there is minimal effect on accuracy. Random, or unrepeatable, movement results in inaccuracy.

[H380]

Full 3-D Finite Element Analysis of a barrel's first few vibration mode shapes and frequencies calculated with the LS-DYNA code.
http://www.varmintal.net/amode.htm

[hwingo]

Hi Guys,

Thanks for all your responses. Much appreciated. Some very interesting answers.

Harold

[epanzella]

The barrel harmonics start as soon as the pressure builds behind the bullet. As with any harmonic wave it has to reverse direction when it reaches maximum defection and it is at this point that the barrel is briefly stationary. Loads tuned to have the bullet clear the rifling during this direction reversal will be the most accurate. The more out of square the parts are to each other (barrel to receiver, receiver to bolt, bolt to barrel) the greater amplitude of the harmonics which will make the gun more "fussy" as far as the loads it will shoot well. Conversely when a gun is "blueprinted", all the mating parts of the rifle are squared as perfectly to each other as humanly possible, reducing the amplitude of harmonics, resulting in a rifle that shoots many loads well. The gun also begins to move from recoil while the bullet is going down the barrel and is another factor that has to be dealt with. This is why gun weight, stock fit, and good shooting form are also important.

[rws]

Vibrations start from firing pin fall, and continue while the bullet goes down the barrel. All guns begin to recoil once the bullets begins to move. There are many things effecting the harmonics.

[GrayTech]

The last stage of accurising is varying the powder charge for a given load until you find a node in the whipping action. The giveaway is a sudden tightening up of your group. If you continue to increase or decrease charge in the same direction, groups will open up again. To achieve this you need repeatability in every other aspect, especially bullet weight.

Sent from my H3123 using Tapatalk
Google will explain the node concept if you wish to research this.

[Yondering]

The barrel harmonics start as soon as the pressure builds behind the bullet. As with any harmonic wave it has to reverse direction when it reaches maximum defection and it is at this point that the barrel is briefly stationary. Loads tuned to have the bullet clear the rifling during this direction reversal will be the most accurate. The more out of square the parts are to each other (barrel to receiver, receiver to bolt, bolt to barrel) the greater amplitude of the harmonics which will make the gun more "fussy" as far as the loads it will shoot well. Conversely when a gun is "blueprinted", all the mating parts of the rifle are squared as perfectly to each other as humanly possible, reducing the amplitude of harmonics, resulting in a rifle that shoots many loads well. The gun also begins to move from recoil while the bullet is going down the barrel and is another factor that has to be dealt with. This is why gun weight, stock fit, and good shooting form are also important.

The last stage of accurising is varying the powder charge for a given load until you find a node in the whipping action. The giveaway is a sudden tightening up of your group. If you continue to increase or decrease charge in the same direction, groups will open up again. To achieve this you need repeatability in every other aspect, especially bullet weight.

Sent from my H3123 using Tapatalk
Google will explain the node concept if you wish to research this.

Lots of good comments and explanations here, but these two are especially on point. Understanding "whip" as vibration and tuning to work with that vibration are key points to accuracy.

[hwingo]

Yondering,
I agree with your comment. There is a lot of good information.

Thanks to all for weighing in on this thread.

Harold

[mihit]

For anyone devolping loads, do "ladder tests" The method is posted online, but generally take the MAX load, subtract 15% and load up in 0.2 grain increments from that number.
Shoot them one after at the same Pont of Aim. You'll get vertical dispersion, with tighter groups at/around certain loads. STOP when you start getting over pressure signs on your cases/primers.
Then pick one of the close groups, pick a load in the middle and work on that- these are your nodes.

I have to disagree with epanzilla, from my reading, the "donut" pressure wave gong down the barrel will cause the muzzle to expand and if the bullet leaves at this point it loses that last bit of stabilisation and can yaw.

[uncle pete]

Barrel vibration would be a more accurate term than barrel whip. At the macro level everything bends and flexes a measurable amount no matter how small the forces or how strong the material is if the measuring equipment has enough resolution and accuracy to measure those forces. And there's little difference between a rifle barrel and a tuning fork. With a 36 x scope I can see my heart beat slightly moving the cross hairs even when using a rest. There's zero doubt those heart beats are also vibrating the barrel all the way out to the tip. Since the speed of sound is over 13,000 mph in steel you can bet the barrel is starting to vibrate as the sear starts to move in the trigger assembly, and certainly between when the trigger breaks and long before the firing pin even hits the primer. The mechanical vibrations within the rifle are impossible to fully eliminate. So as others have already pointed out finding a bullet weight and shape, seating depth, powder type, burn speed and amount, primer as well as paying attention to absolute reloading consistency allows fine tuning of those vibrations so the muzzle is at the same vibration point as much as possible. There's a whole lot more going on within any gun before the primer ignites than most seem to think. Yes the major vibrations are caused by the primer and powder ignition, gas expansion and the bullet acceleration until it leaves the barrel. But there's still other causes that should be considered as well.