Barrel whip effect?

[Jeff Porter]

I do not expect bullets of different weights and velocities to impact at the same point onf the target but what I saw today may be a good example of what happens whan a barrel is not in a happy place for a bullet. These are not loads that have been worked up for this rifle, just ammo that is left form a couple of other projects.

I am playing with a new R700 SPS in .308 with a 22" 1:10 pencil barrel. I got a preliminary " zero" on the scope with the dial set to the middle of travel on both windage and elevation using the IMI RazorCore 175 SMK load at 2450 fps. It was about 1.6" high with good windage. ( Orange dot)

I then proceed to shoot five other groups with ammo from old lots I had in the ammo box ranging from 110gr to 180 gr. with Varget, 748, I-4895, H4895 and 8208.

125 TNT at 2970 fps (purple) and a 155 Palma at 2850 fps (yellow) kept windage the same but lower POI as expected for much faster loads.

110 Vmax (Gray) was the fastest load at 3300fps but it is up and right 1.5" , 110 Nosler at 3000 fps ( Green) was down and left a bit and the 180 Nosler BT (Lt. Blue) was way up and left at 2425 fps.

Not sure what it really shows but it caught my eye.

My guess is the three loads in the vertical stack in the middle are in a quieter place in the barrel vibration than the three outliers.

Any other ideas?

 

[Straightshooter1]

I do not expect bullets of different weights and velocities to impact at the same point onf the target but what I saw today may be a good example of what happens whan a barrel is not in a happy place for a bullet. These are not loads that have been worked up for this rifle, just ammo that is left form a couple of other projects.

I am playing with a new R700 SPS in .308 with a 22" 1:10 pencil barrel. I got a preliminary " zero" on the scope with the dial set to the middle of travel on both windage and elevation using the IMI RazorCore 175 SMK load at 2450 fps. It was about 1.6" high with good windage. ( Orange dot)

I then proceed to shoot five other groups with ammo from old lots I had in the ammo box ranging from 110gr to 180 gr. with Varget, 748, I-4895, H4895 and 8208.

125 TNT at 2970 fps (purple) and a 155 Palma at 2850 fps (yellow) kept windage the same but lower POI as expected for much faster loads.

110 Vmax (Gray) was the fastest load at 3300fps but it is up and right 1.5" , 110 Nosler at 3000 fps ( Green) was down and left a bit and the 180 Nosler BT (Lt. Blue) was way up and left at 2425 fps.

Not sure what it really shows but it caught my eye.

My guess is the three loads in the vertical stack in the middle are in a quieter place in the barrel vibration than the three outliers.

Any other ideas?

View attachment 1408966

Be aware to not confuse barrel whip with barrel vibration, they're very different things happening at different times. Like in videos, especially slow motion, one can see barrel whip, but barrel vibration moves down the barrel at the speed of sound in steel and almost impossible to be seen unless you've got the right equipment.

 

[1raggedhole]

I’m always amazed by POI variation with different loads. It seems to get worse as barrel gets skinnier. Heavy bull barrels tend to have less variation in my experience. That would support the barrel vibration or whip theories.
I have an x-bolt hells canyon speed that requires a new zero with almost any load change. Very few have similar POI, even with similar bullet weight and speed.

 

[Straightshooter1]

I’m always amazed by POI variation with different loads. It seems to get worse as barrel gets skinnier. Heavy bull barrels tend to have less variation in my experience. That would support the barrel vibration or whip theories.
I have an x-bolt hells canyon speed that requires a new zero with almost any load change. Very few have similar POI, even with similar bullet weight and speed.

Since I first heard about barrel harmonics, I've been going OCD to try and understand what's going on with it and to say the least, it's actually very complex the way impulses travel back and forth at the speed of sound in steel. To understand on the simple side of it, the pic below should give you some idea about why you see those variations as it having to do with where the muzzle is pointing at a particular time with the vibration:


PS: The "whip" of the barrel that we can often see, especially in slow motion, occurs well after the bullet has cleared the muzzle. It's the other higher frequency harmonic modes at work that's producing such variances.

 

[1raggedhole]

Since I first heard about barrel harmonics, I've been going OCD to try and understand what's going on with it and to say the least, it's actually very complex the way impulses travel back and forth at the speed of sound in steel. To understand on the simple side of it, the pic below should give you some idea about why you see those variations as it having to do with where the muzzle is pointing at a particular time with the vibration:
View attachment 1409161

Agreed. Here is an interesting link to an analysis by a smart guy, varmint Al:

Barrel Harmonics Mode Shape Movies

 

[Jeff Porter]

Since I first heard about barrel harmonics, I've been going OCD to try and understand what's going on with it and to say the least, it's actually very complex the way impulses travel back and forth at the speed of sound in steel. To understand on the simple side of it, the pic below should give you some idea about why you see those variations as it having to do with where the muzzle is pointing at a particular time with the vibration:
View attachment 1409161

Is the node at the center of travel where the barrel wave is moving the fastest or at the crest or trough of the wave where it slows and reverses direction? Seems to me it would be the most consitent for a longer time at the crest and troughs as it slows down.

 

[Straightshooter1]

Is the node at the center of travel where the barrel wave is moving the fastest or at the crest or trough of the wave where it slows and reverses direction? Seems to me it ould be the most consitent for a longer time at the crest and troughs as it slows down.

If you put that sine wave picture in motion, the top and bottom peaks (the anti-nodes) move up and down, or back and forth, to put it simply, from peak to peak, but there's no movement at "the center of travel". . . the node of the sine wave.

Maybe this explanation can help:

 

[Idaho-Lefty]

I get very Little, POI "shift" from my STIFF 24 inch, HEAVY Sporter, .707 Dia. Muzzle, 6 XC Criterion Barrel that's, Pillar and Glass Bedded, in a H-S Precion stock, with, 1.5 inches of, "Shank" bedded, rest of, bbl is, "Free floated".
It's NOT a total, "Truck Axel" Barrel at, 9.5 pounds, Total scoped Rifle, weight.
The 107 gr. BTHP Match, Sierra's, are only, a 1/2 inch right of, the 103 gr. Hornady, ELD- X's that, I will use for, Coyotes ( just, 2 scope Clicks ). And, the Bullets "Print" to exact, SAME, POI,.. Week to Week !
I'm Very Happy with this, Weight / Size of, Barrel for,.. Targets and Varmints.
Pencil Barrels, are Fine for, Deer / Elk Hunting,.. IF, a couple of, "Cold Bore" shots, ARE,.. "Good" !
We ( My Family ) have, NO major, POI "Shift Issues" using, 7.5 lb. Tikka's for, Hunting, Big Game.
But, we are, "Religious" about, "Cold Bore" testing,.. PRE- Hunt.
Be Aware of, Barrel Harmonic's and just know,.. HOW to,... "Tame",.. it !

 

[Jeff Porter]

If you put that sine wave picture in motion, the top and bottom peaks (the anti-nodes) move up and down, or back and forth, if you will, from peak to peak, but there's no movement at "the center of travel". . . the node of the sine wave.

Hmmm - Not sure I agree. There is maximim movement at the mid line of the sine wave.

-

In that video looking only at the vertical velocity of the dot on the sine wave, it is moving the fastest at the center line and slowest at the peaks and troughs.

Edit to add - if you could go to the right side of your computer monitor and look at the sine wave coming at you the path would look up and down with speeding up in the middle and slowing down when it changes direction.

Wave motion and circular motion are related. If you look at circular motion from the side instead of the top, think of a pingpong ball going around on a record player, the pingpong ball would look as if it is moving from one side to the other slowing down and turning around then accelerating to the other and slowing down and turning around.

Maybe we are saying the same thing but 90 degree out of phase?

 

[CharlieNC]

Positive compensation . Because faster bullets should impact higher, when the barrel is on the upswing the faster leaves earlier, and the slower after the muzzle is pointing higher. This is only a few thousands of an inch movement by the muzzle, and vibrating at the speed of sound.

 

[Jeff Porter]

Positive compensation . Because faster bullets should impact higher, when the barrel is on the upswing the faster leaves earlier, and the slower after the muzzle is pointing higher. This is only a few thousands of an inch movement by the muzzle, and vibrating at the speed of sound.

If the bullets are the same ? correct? This shows the heaviest, slowest bullet with the maximum POI with the same sight settings.

What if your barrel composition and timing is such that the sine wave is moving in a direction other than up and down?

What about compression waves in addition to the sine waves? Do thay all have the same velocity and frequency or are these affects competing at the muzzle?

 

[Jeff Porter]

Maybe there is some conflation of traveling sine waves with standing waves. Standing wave nodes are at the midline.

 

[CharlieNC]

If the bullets are the same ? correct? This shows the heaviest, slowest bullet with the maximum POI with the same sight settings.

What if your barrel composition and timing is such that the sine wave is moving in a direction other than up and down?

What about compression waves in addition to the sine waves? Do thay all have the same velocity and frequency or are these affects competing at the muzzle?....

There are many transverse bending frequencies which occur, but these are so slow the bullet has exited the barrel in around 1.5milli-seconds before they become significant. I don't know about compression, but a force is transmitted longitudinally at the speed of sound, back and forth about the muzzle. I wrote a length report about this around three weeks ago, with more info than you probably want to know!

 

[gunsandgunsmithing]

Here's a good thread on here about tuning involving a very sharp guy, GSPV, who is a degreed engineer. Keep in mind that his powder charge illustration is just opposite of what you see with tuners, which should be self explanatory if you think about it because when we increase powder, we're speeding up bullet exit time. When we move a tuner, we can speed or slow where the bbl is in relation to exit time. They allow us to change "phase time". Yes, that's a real thing. In simplest terms, it means that we literally move the top or bottom of the sine wave left or right to coincide with bullet exit. Yes, we talk in terms of "nodes" in this game but the anti-node is where you want to be.
Enjoy. It's not terribly long and has a lot of good info, tuner or not. Tuning IS about timing bullet exit and muzzle position when it happens. It's not voodoo and shouldn't be as controversial as it is.

Load Data for 6mm PPC

I use from 29.2-29.7 V133. Some guys are slightly above 30. As most of you know different loads for different conditions.

forum.accurateshooter.com

 

[Straightshooter1]

Hmmm - Not sure I agree. There is maximim movement at the mid line of the sine wave.

-

In that video looking only at the vertical velocity of the dot on the sine wave, it is moving the fastest at the center line and slowest at the peaks and troughs.

Edit to add - if you could go to the right side of your computer monitor and look at the sine wave coming at you the path would look up and down with speeding up in the middle and slowing down when it changes direction.

Wave motion and circular motion are related. If you look at circular motion from the side instead of the top, think of a pingpong ball going around on a record player, the pingpong ball would look as if it is moving from one side to the other slowing down and turning around then accelerating to the other and slowing down and turning around.

Maybe we are saying the same thing but 90 degree out of phase?

That's a whole different sine wave motion than what you get with standing wave with vibration/harmonics.

 

[gunsandgunsmithing]

That's a whole different sine wave motion than what you get with standing wave with vibration/harmonics.

Granted, yes, it's very much oversimplified but I'm not sure what you're specifically addressing. So, I can't agree or disagree. Not many will ever watch it live on an o-scope but we can all see what matters, on target. On target, it appears over simplified too. It does appear on target as a relatively smooth sine wave. In the real world, it's anything but a simple, smooth waveform. There are muliple frequencies going on at once and the longitudinal aspect...and radially, all happening at the speed of sound in steel, which is far greater than the sine wave or frequency near the muzzle will represent...depending on equipment used to measure, to a large degree, I'm sure.

 

[Jeff Porter]

That's a whole different sine wave motion than what you get with standing wave with vibration/harmonics.

Now I am confused. Which are you referring to in your first post? A sine wave or a standing wave?

 

[Straightshooter1]

Now I am confused. Which are you referring to in your first post? A sine wave or a standing wave?

The standing wave, which a barrel naturally vibrates to at a frequency (or multiple frequencies).

 

[Straightshooter1]

Granted, yes, it's very much oversimplified but I'm not sure what you're specifically addressing. So, I can't agree or disagree. Not many will ever watch it live on an o-scope but we can all see what matters, on target. On target, it appears over simplified too. It does appear on target as a relatively smooth sine wave. In the real world, it's anything but a simple, smooth waveform. There are muliple frequencies going on at once and the longitudinal aspect, all happening at the speed of sound in steel, which is far greater than the sine wave or frequency near the muzzle will represent...depending on equipment used to measure, to a large degree, I'm sure.

Yes, over simplified as the vibration is quite complex as 1raggedhole's link to an illustration shows. The complex resonance gets to the muzzle long before the bullet, because of the speed through steel. The bullet traveling down the bore is changing what happening at the muzzle all along the way until it exits. Regardless of the complexity of the resonance, the barrel is still subject to the resonance vibrations that's natural to the barrel, which moves as a standing wave.

 

[gunsandgunsmithing]

Yes, over simplified as the vibration is quite complex as 1raggedhole's link to an illustration shows. The complex resonance gets to the muzzle long before the bullet, because of the speed through steel. The bullet traveling down the bore is changing what happening at the muzzle all along the way until it exits. Regardless of the complexity of the resonance, the barrel is still subject to the resonance vibrations that's natural to the barrel, which moves as a standing wave.

I agree. The way I look at it is this and it's based on doing vibration analysis and seeing what happens on target....seeing bullet exit relative to muzzle position. A tuner being at the end of the bbl is adjusting for the "average" of what's going on behind it, consistently. Yes, that's probably an oversimplification too but it works on target, agrees with vibration analysis and it explains why such small movements of a tuner can affect phase time without significantly altering frequency. There is still a lower "natural frequency" that overplays the multiple higher freqs at work due to forced deformation. It can be seen with something as simple as a guitar tuner while exciting the bbl.
Obviously, a guitar tuner won't tell you all that's going on, only what it hears and can define...the "average"....or "natural" freq.