Barrel harmonics in plain english

[jelenko]

I think many people would disagree with your first statement. If that is truly the case, why do "tuners" work?

I'm not familiar with using a tuner.
Do tuners reduce barrel whip?

FYI. Here's a slo mo of an M14 - from 37 secs on you can see the bullet leave the barrel before the barrel starts to flex.

 

[Hi-NV Shooter]

The 'whip' in the barrel doesn't reach the muzzle before the bullet has left the barrel.

Chris Long developed a theory based on the same concept as this video.
Because accuracy nodes are found with differences in barrel time [the time a bullet is in the barrel] in the 10's of microseconds, he ruled out barrel whip because it's oscillations are too slow to account for accuracy node so close together in terms of the time the bullet is in the barrel.

Question, he based ii on theory, so how did he rule out anything without practical (working experience) knowledge?

Lee

The 'whip' in the barrel doesn't reach the muzzle before the bullet has left the barrel.

Chris Long developed a theory based on the same concept as this video.
Because accuracy nodes are found with differences in barrel time [the time a bullet is in the barrel] in the 10's of microseconds, he ruled out barrel whip because it's oscillations are too slow to account for accuracy node so close together in terms of the time the bullet is in the barrel.

 

[Straightshooter1]

I think your terminology is off. Your practical understanding may be correct but the wording of that statement is incorrect.

View attachment 1312782
A wave node cant be at the muzzle end because it is unsupported. The muzzle will always be an antinode for the different standing harmonic vibration modes in a free floated rifle barrel supported on one end (the action).

A good analogy for the position of the muzzle of a rifle barrel is a pendulum. The muzzle is moving the fastest in the middle (neutral unflexed strait position) of its wave. After the barrel crosses that center of the wave it begins to progressively slow down until it stops at its maximally flexed position and reverses direction. It starts to speed up from that point achieving max velocity as it crosses the unflexed center point and starts the process again going to the other max flexed side. The blue graph shows velocity vs time for these positions and the red graph shows the position vs time. You can see at the bottom position (D) the velocity is at max in the blue graph and has the neutral position in he red graph. And you can see the sides (A&G) have zero velocity in the blue graph and peak positions on the red graph.
View attachment 1312787
The two best positions are the max flexed positions. Close range bench rest guys will likely tune with shots falling as close to the peak as possible. BAB positions and GFG positions and exit timings as those spots have the least muzzle movement vs time hence the best raw accuracy.

Long range shooters need to use positive compensation to limit their vertical due to velocity spread so they likely tune on GFE or CBA positions and timings to insure their slower bullets are launched at a slightly higher angle to add some of the lost elevation at long range due to being slower.

Tuners do a few things. They do change the node points but that's a secondary concern really as some barrel movement is good for accuracy at extended ranges. The primary effects are these.

They lower the frequency of the vibrations making tuning windows larger.

They lower the amplitude of vibrations in the horizontal plane and give the barrel a more vertically oriented vibration pattern.

They allow you to change the vibration frequencies to change the point on the wave the bullet exits without having to adjust the seating depth of the bullet or powder charge. A simple dial on the end of the muzzle can make fine changes to where on the wave the bullet exits but does not change the bullets actual exit time to an appreciable degree.

Yeah, I got it backwards. Thanks for clarifying that regarding the speed and position of the node and antinode. My physics is pretty rusty these days. These old brain cells of mine don't work as well as they used to.

 

[darkangel_r2]

Does a tuner increase the amplitude in the vertical plane?
-

I purposely left out that info because I'm not sure.

I think Mike Ezell said that they can.

I would think it depends on the balance and recoil of the rifle. If the rifle is well balanced and the net recoil force is close to the bore axis I would think that having to move the extra mass of the tuner would make it similar or less in amplitude. If the recoil is significantly far from the bore axis I would assume the amplitude would be greater. This part is speculation on my part so I'd ask the manufactures.

 

[Brians356]

I purposely left out that info because I'm not sure.

I think Mike Ezell said that they can.

All else being equal, it seems perhaps lowering frequency would increase amplitude, but I never studied formal mechanics.
-

 

[darkangel_r2]

I'm not familiar with using a tuner.
Do tuners reduce barrel whip?

FYI. Here's a slo mo of an M14 - from 37 secs on you can see the bullet leave the barrel before the barrel starts to flex.

That's a lower order (higher amplitude lower frequency) vibration mode. From vaughns rifle accuracy book ch4 pg 84-87 worked examples of the typical benchrest rifle will have tuning frequencies somewhere around 6-10k Hz. If what we are seeing in that video is 1/2 a cycle and it takes 1.25ms to finish its frequency is around 400hz. Which is not in the ballpark of the tuning frequencies. vaughns, varmintAI, Kolbe ect. all put the max amplitude of a target rifle muzzle's vibration while the bullet is in the bore on the order of 0.004".

Rifle Accuracy Facts Full V 1.0 ( First Full Scan) : Harold R. Vaughn : Free Download, Borrow, and Streaming : Internet Archive

The author, who spent his career studying trajectories of nuclear missles and artillery shells, wrote this work after becoming dissatisfied with the accuracy...

archive.org

Barrel Tuner Analysis -- FEA Dynamic Analysis of Esten's Rifle with/without a Tuner.

What we are seeing in that video is the lowest order (no anti node) vibration pattern induced by preloaded gravity of the barrel on the receiver and recoil. You can tell because it also happens when the bolt closes.

 

[darkangel_r2]

All else being equal, it seems perhaps lowering frequency would increase amplitude, but I never studied formal mechanics.
-

From varmintAIs estens rifle page it looks like the total amplitude is very similar with and without the tuner. I think thats what we will find in a well balanced rifle with the net recoil near the bore axis. Amplitude varier from .47" to .5" pretty tight spread.

 

[snert]

I sat thru a lecture once regarding tuning a load and barrel harmonics. Guywas a genius. i am not.

When all done I had it figured...

I recalled being in the locker room in 7th grade coming out of the mandatory shower with 9th grade boys leaving. In simple terms, you want to be either close to the towel, or just outta reach, cause if the whip (harmonics) is just right its gonna land and sting like heck. Of course as a shooter, you want perfect harmonics...oh to be in 9th grade!

Now thats harmonics for dummies

 

[chop house]

BAB positions and GFG positions

good illustrations. likely you meant "FGF".

great responses from all. one point of my op was to indicate the true complexity of the issue and grab a way to conceptualize what is happening in the barrel steel.

hope the title wasn't too much clickbait.

 

[darkangel_r2]

good illustrations. likely you meant "FGF".

Thank you yes that's correct.

great responses from all. one point of my op was to indicate the true complexity of the issue and grab a way to conceptualize what is happening in the barrel steel.

If you are competing at a specific distance a repeated ladder test at that distance can tell you everything you need to know. If you only have access to short range load testing getting a target analysis app like on target or similar and just plotting how the centers of your group move with increasing charge weight can accomplish the same thing with a few more shots and some time in excel.

 

[ben lurkin]

That’s a very poor analogy to barrel harmonics. He’s using compressional forces and the physical properties of the material to describe how a compressional wave travels through a solid. The response he is seeing is that wave being reflected back as a result of the end of the barrel. That’s not what we’re really interested in.

What we’re chasing is barrel harmonics. In layman’s terms, think about a plucked guitar string. The length and diameter (and tension) of the string determines the vibration/tune of the string. In a mathematical sense, If you look at a sine wave to represent muzzle deflection, you want the bullet to exit that muzzle when it is at it’s maximum amplitude. Once we find that, a slight timing change in velocity will result in the muzzle being in essentially the same spot. As an example, the “sweet spot” of a barrel is when sin(90)=1. Now let’s take a 15 degree variance, Sin(75 or 105)= 0.966; a difference of only 0.034. Now if the barrel is at it’s natural, “unplucked” position, Sin(0)=0, using the same 15 deg variation, sin(15)=0.25. (For the purists, I realize angular measurements aren’t quite “correct”). Note the same 15 degree change yielded over 7x greater deflection. This is the essence of latter testing your loads is doing for you.

 

[boltfluter]

That’s a very poor analogy to barrel harmonics. He’s using compressional forces and the physical properties of the material to describe how a compressional wave travels through a solid. The response he is seeing is that wave being reflected back as a result of the end of the barrel. That’s not what we’re really interested in.

What we’re chasing is barrel harmonics. In layman’s terms, think about a plucked guitar string. The length and diameter (and tension) of the string determines the vibration/tune of the string. In a mathematical sense, If you look at a sine wave to represent muzzle deflection, you want the bullet to exit that muzzle when it is at it’s maximum amplitude. Once we find that, a slight timing change in velocity will result in the muzzle being in essentially the same spot. As an example, the “sweet spot” of a barrel is when sin(90)=1. Now let’s take a 15 degree variance, Sin(75 or 105)= 0.966; a difference of only 0.034. Now if the barrel is at it’s natural, “unplucked” position, Sin(0)=0, using the same 15 deg variation, sin(15)=0.25. (For the purists, I realize angular measurements aren’t quite “correct”). Note the same 15 degree change yielded over 7x greater deflection. This is the essence of latter testing your loads is doing for you.

That's a great explanation, on a very complex topic. Thanks for sharing!

Paul

 

[fx77]

And what is the effect of heat in the barrel harmonics with successive shots?
theoretically a factor in practice just do not know.

 

[jelenko]

Question, he based ii on theory, so how did he rule out anything without practical (working experience) knowledge?

Lee

Great question. A theory is only as good as it's predictions match reality.
Chris is a shooter and did test the theory.
You can read about it with a search on "Chris Long Bullet Time".

 

[Uthink Uknow]

Fisicks be damned.
I check my target and turn the tuner to get all the shots on the same vertical plane.

 

[Alexander-M]

<<<<<<PARTIAL QUOTE >>>>> (/Alex)
Tuners do a few things. They do change the node points but that's a secondary concern really as some barrel movement is good for accuracy at extended ranges. The primary effects are these.

They lower the frequency of the vibrations making tuning windows larger. UNDERSTOOD / Alex

They lower the amplitude of vibrations in the horizontal plane and give the barrel a more vertically oriented vibration pattern. HOW ? / Alex

I am in no way challenging what you stated, but simply asking how does a tuner lower the amplitude in the horizontal plane and not in both planes simultaneously?
Thanks!
Alex

 

[AckleymanII]

Back many years ago when I was visiting Ed Shilen about the Hewland trans in his Formula Ford race car we got on a different subject. His idea was to tune the barrel from a ringing sound to a thud. He brought out electronic headphones with a small mic on it. He told me to put them on and use the little microphone to listen to the barrel as he tapped it with a brass rod. I adjusted on the tuner until the ring turned to a thud.
Does it work? I don't know, but I own the headphones.

Along those same lines, take a 12"x 3/4" piece of brass rod, tap the barrel, and listen to the ring. If you hear a dead spot, do not cut the barrel within 2" of that dead spot...won't shoot well if you do. Reason, inclusion in the steel. You sure do not need any headphones to hear the ring.

I will try Butch's method.

 

[darkangel_r2]

I am in no way challenging what you stated, but simply asking how does a tuner lower the amplitude in the horizontal plane and not in both planes simultaneously?
Thanks!
Alex

The tuners mass at the end of the barrel induces a larger droop in the barrel due to gravity and adds to the droop present from the barrels own weight. But the muzzle is an anti node putting that mass on the anti node dampens harmonics. Think about touching the open end of a tuning fork vs letting it ring free. The vibrations have to move more mass so unless they are given more energy to start with (more droop in the vertical plane) they will have less amplitude since they have to move more mass.

Since the tuner does nothing to add to the horizontal imbalance of a rifle barrel it does not induce stronger horizontal vibrations. Since the horizontal vibrations are the same strength with and without the tuner (close enough anyway) the extra mass of the tuner preferentially dampens those vibrations.

Tuners add to the vertical imbalance in the barrel and induce more energetic vertical vibrations. But those increased energy vibrations have to move more mass again so the net effect is near a wash in terms of amplitude (can be rifle dependent I think so ask a manufacturer for sure) but now you have eliminated some horizontal and gained more precise mechanical control over where on a vertical vibration wave your bullet leaves and lengthened your tuning window. These things are a significant benefit.

 

[PigButtons]

Thanks to all who have contributed to this thread, good mental exercise. I think anyone with positive experiences using a tuner will intuitively understand the benefits.

The gap between theory and practice was made legend by Yogi Berra. But what I don't see in all of this technical analysis is the Calculus to account for the effects of the projectile pushing it's way through the press fit bore. Much as a boat pushes up a bow wake, the bullet must push a deformation through the length of the barrel.

All that tells me is that the only calculation that matters is repeatable POI. Everything else is less predictable than merits consideration when pressing the bang switch. No offense intended. Just venting my confusion wrapped in ignorance.

 

[Straightshooter1]

Thanks to all who have contributed to this thread, good mental exercise. I think anyone with positive experiences using a tuner will intuitively understand the benefits.

The gap between theory and practice was made legend by Yogi Berra. But what I don't see in all of this technical analysis is the Calculus to account for the effects of the projectile pushing it's way through the press fit bore. Much as a boat pushes up a bow wake, the bullet must push a deformation through the length of the barrel.

All that tells me is that the only calculation that matters is repeatable POI. Everything else is less predictable than merits consideration when pressing the bang switch. No offense intended. Just venting my confusion wrapped in ignorance.

lol . . .well, there's very few on this website might understand this:
But I'd bet that the calculus has indeed been done for for the effects of a projectile going down a bore. Me, I probably can't even solve a simple differential equation anymore.

Repeatability and confirmation is the basis of Scientific Theory. Today, we have better guns, powder, scales, projectiles and results because of it, even if we don't understand the science. It's an ongoing process and the results keep getting better (though in progressively smaller increments).