Barrel Harmonics Associated With The Target

[gunsandgunsmithing]

i don't know about where you shoot,but at the ranges I've shot at the air density is constantly changing. I keep a temp/humidity guage on my bench always. The air density even changes at different places on the range. Air density is different in the shade than downrange in the sun. Temp swings of 20-25F and humidity changes of 20-30percent in 2 hrs is not uncommon.......would drive me crazy making tuner adj'ts.
I've found using wind flags helps me more than anything.

I only move the tuner if the target tells me to. Why would I not? IME, density is only one variable. Temp seems to be most important but temp and density changes aren't always linear. There are whole days that I never touch the tuner and days that I do. The adjustments are small, only a mark or two over the whole day, when needed. Again, there are days it stays put, even over the same temp swings because density has an offsetting effect to temp. Powders are a big variable as some are more temp stable than others but none are perfect. So, some loads will require a little more attention to changes than others. In short range it's easy enough..just watch and tune by the sighters. It's easy. People really tend to overthink tuners rather than just getting out there and learning how to use them. Everyone wants an easy button...a formula that's 100% right on. Same with powder tuning but how long have we been doing it without that formula. Just shoot and either change the load or move the tuner as needed. As a rule, I don't move the tuner unless I'd change loads.

 

[CharlieNC]

I understand that this initial report covered too many aspects on the topic of harmonics, and I should have broken this out into at least two separate reports.

First question, which is my primary focus: DOES MY CALCULATION PROCEDURE TO CALCULATE BARREL VIBRATION FREQUENCY, AMPLITUDE, and PHASE SHIFT FROM THE TARGET APPEAR ACCURATE? If we can pass this step as part 1, then it will be simpler to move forward into the intrepretation of the resuts.

 

[gunsandgunsmithing]

I understand that this initial report covered too many aspects on the topic of harmonics, and I should have broken this out into at least two separate reports.

First question, which is my primary focus: DOES MY CALCULATION PROCEDURE TO CALCULATE BARREL VIBRATION FREQUENCY, AMPLITUDE, and PHASE SHIFT FROM THE TARGET APPEAR ACCURATE? If we can pass this step as part 1, then it will be simpler to move forward into the intrepretation of the resuts.

I'm still not 100% sure what you're attempting to do. Is it to calculate frequency/amplitude/phase shift based on a picture of a target at a known distance, etc? I think that could be done to a degree but there are lots of variables and would only apply directly to that particular gun, conditions etc. Lots of noise in that calculation but am I understanding your goal right? If so, even an inexpensive accelerometer might be easier and more accurate. Just my thoughts

 

[Beiruty]

So does it surprise you that all that the bending frequencies modeled by Al and others are not the ones observed on the target, but harmonics of the speed of sound? Long did not study poi, but conjectures regarding group size. Faster bullets hit lower on a target and Kolbe is the only one I've seen that actually instrumented a barrel to correlate with the shot vs just comparing to a calculation, to demonstrate positive compensation. None of this provided a clear characterization of what we observe, which is why I undertook this study a couple of years ago, from a quantitative perspective vs conjecture. At this point I don't propose to have all of the answers, but once again a method to analyze a target to help develop understanding.

I totally agree. Such effort to harmonize all the rfile/load factors on the accuracy (POI vs POA) is a matter of resources: Time, money, and dedication.

We shouldn't forget extreme accuracy is important at very long range while shooting small targets. "long" and "small" are all relative to the shooting application,

How Much Does It Matter? Overall Summary

As long-range shooters, we tend to obsess over every little detail. After all, we’re trying to hit r...

precisionrifleblog.com

 

[CharlieNC]

I'm still not 100% sure what you're attempting to do. Is it to calculate frequency/amplitude/phase shift based on a picture of a target at a known distance, etc? I think that could be done to a degree but there are lots of variables and would only apply directly to that particular gun, conditions etc. Lots of noise in that calculation but am I understanding your goal right? If so, even an inexpensive accelerometer might be easier and more accurate. Just my thoughts

Yes. A ladder test that covers 8-10% charge weight will exhibit a range where the vertical POI is is flat or even goes down on the target. I quoted two such examples from Vaughn's book where he stated if the effect of gravity is calculated away, then the results are a sinusoidal wave of certain frequencies; I have simply presented the calculations to perform these operations (which he did not offer) in order to examine more targets to answer the questions you pose. For example my limited data suggests bullet weight has a significant effect on the amplitude of vibration.

I have begun testing with an accelerometer, and show one initial example. My limited experience, and the results of Vaughn, demonstrate that not only that multiple frequencies exist but that there are also transient effects at the initial point of firing. But in any case the primary question is what is the dominant harmonic which the target exhibits, and knowing that utilize the accelerometer as a tool vs the answer to aid in understanding.

 

[CharlieNC]

I totally agree. Such effort to harmonize all the rfile/load factors on the accuracy (POI vs POA) is a matter of resources: Time, money, and dedication.

We shouldn't forget extreme accuracy is important at very long range while shooting small targets. "long" and "small" are all relative to the shooting application,

View attachment 1398551

How Much Does It Matter? Overall Summary

As long-range shooters, we tend to obsess over every little detail. After all, we’re trying to hit r...

precisionrifleblog.com

I do not discount the fact there are many important factors affecting accuracy and address them during my shooting practices, but for the sake of this investigation I'm not interested in those other factors. I am simply trying to characterize barrel harmonics using the resuts of a ladder test on the target; call this nerdy or insignificant in the grand scheme, but this is the only aspect of concern for this post.

 

[gunsandgunsmithing]

Yes. A ladder test that covers 8-10% charge weight will exhibit a range where the vertical POI is is flat or even goes down on the target. I quoted two such examples from Vaughn's book where he stated if the effect of gravity is calculated away, then the results are a sinusoidal wave of certain frequencies; I have simply presented the calculations to perform these operations (which he did not offer) in order to examine more targets to answer the questions you pose. For example my limited data suggests bullet weight has a significant effect on the amplitude of vibration.

I have begun testing with an accelerometer, and show one initial example. My limited experience, and the results of Vaughn, demonstrate that not only that multiple frequencies exist but that there are also transient effects at the initial point of firing. But in any case the primary question is what is the dominant harmonic which the target exhibits, and knowing that utilize the accelerometer as a tool vs the answer to aid in understanding.

Dominant frequency....I look at it as the average of many frequencies going on at once, behind the tuner. It does appear that only one shows up on the target with or without a tuner, though. But I think I'm following you somewhat better now. Cool stuff!

 

[jvw2008]

Charlie I want to commend you on your efforts so far. You have obviously put a lot of research, thought, and personal work into this project. Sometimes folks who armchair nitpick are simply speaking up to toot their own horn. Others raise challenging points which help us refine our thinking in the pursuit of a correct answer. I think I see a little bit of both in this thread so far.
An accurate description of the physical mechanics associated with internal ballistics is a very worthwhile pursuit but I think we are still fumbling our way through it at this point. The individuals you have sighted in your paper have provided valuable insight but probably not theories which are 100% correct.
As I see it, you are simply trying to use target data to plug into a formula which will have some amount of predictive value for successful development of an accurate tune. I guess I’m not concerned about the “noise” that formula doesn’t account for, as long as the generated predictions hold. Like Long’s OBT, you are not trying to generate something that is 100% accurate, just something predictive. I’m not totally sold yet but you sure have my curiosity amped up.
Carry on. Let’s hear more.

 

[gunsandgunsmithing]

Charlie I want to commend you on your efforts so far. You have obviously put a lot of research, thought, and personal work into this project. Sometimes folks who armchair nitpick are simply speaking up to toot their own horn. Others raise challenging points which help us refine our thinking in the pursuit of a correct answer. I think I see a little bit of both in this thread so far.
An accurate description of the physical mechanics associated with internal ballistics is a very worthwhile pursuit but I think we are still fumbling our way through it at this point. The individuals you have sighted in your paper have provided valuable insight but probably not theories which are 100% correct.
As I see it, you are simply trying to use target data to plug into a formula which will have some amount of predictive value for successful development of an accurate tune. I guess I’m not concerned about the “noise” that formula doesn’t account for, as long as the generated predictions hold. Like Long’s OBT, you are not trying to generate something that is 100% accurate, just something predictive. I’m not totally sold yet but you sure have my curiosity amped up.
Carry on. Let’s hear more.

I'm all for anything that isn't simply bs by people with zero experience using tuners. I make posts on tuning because of so much bs, not to incite more of it. I have a lot of experience with and I've done a lot of testing regarding tuning. Is that blowing my horn or supporting my position over the "non-science" bs out there so often posted by people with little or no experience? I guess you can do like we have/are and do the testing the way you think it should be done. Same for anyone, testing for yourself is golden. That's how we know things. And I agree...kudos to Charlie for his work. Good info invariably shortens the learning curve.

 

[Old Navy]

This makes my head hurt.

I hope there is no test at the end of class.

 

[gunsandgunsmithing]

I hope there is no test at the end of class.

There always is....how'd ya shoot today?

 

[Old Navy]

There always is....how'd ya shoot today?

To cold, wet and muddy to get out.

 

[CharlieNC]

Charlie I want to commend you on your efforts so far. You have obviously put a lot of research, thought, and personal work into this project. Sometimes folks who armchair nitpick are simply speaking up to toot their own horn. Others raise challenging points which help us refine our thinking in the pursuit of a correct answer. I think I see a little bit of both in this thread so far.
An accurate description of the physical mechanics associated with internal ballistics is a very worthwhile pursuit but I think we are still fumbling our way through it at this point. The individuals you have sighted in your paper have provided valuable insight but probably not theories which are 100% correct.
As I see it, you are simply trying to use target data to plug into a formula which will have some amount of predictive value for successful development of an accurate tune. I guess I’m not concerned about the “noise” that formula doesn’t account for, as long as the generated predictions hold. Like Long’s OBT, you are not trying to generate something that is 100% accurate, just something predictive. I’m not totally sold yet but you sure have my curiosity amped up.
Carry on. Let’s hear more.

You have accurately pegged the intent of my effort, which is at an early stage of development; thank you for the encouragement. Using this as a characterization tool, there is a framework to assess what parameters affect the barrel harmonics and then learn how to harness them to our advantage. As mentioned the harmonic window we can utilize is a function of frequency and amplitude which determine the size of the node, and at this point there are a couple of features that I find interesting and not explainable:

1. While the frequencies are associated with the speed of sound, why does the target reflect the higher order harmonics which result in a narrower node?

2. Why does the amplitiude correlate highly with the bullet weight?

More data from "good" ladder tests is needed to begin to understand these and who knows what other features. If anyone has ladders spanning a good charge weight range, and exhibiting a nice node, I would appreciate them sharing the data with me for this analysis and into the data base.

In the meanwhile I will explore more using the high speed accelerometer.

 

[CharlieNC]

What is the 'modification' that was applied from Long's theory to the last/third method? Is it just the idea that transverse waves are also created that travel at the speed of sound?

And, the 'fact' that the harmonic slope varies by distance to the target would explain why loads that are accurate at short range are much worse at long range! It doesn't have to do with the bullet 'going to sleep'. For me, very cool.

That is a good question with a couple of facets to answer:

Firstly Long only discusses group size as related to a muzzle disburbance, as recently as a few days ago on Eric Cortina's youtube. Never any association to positive compensation which clearly plays a major as related to charge weight ladders.

Secondly the ladder frequencies observed on the target, due to positive compensation, from what I have seen all relate to the speed of sound which is the basis of Long's work. To me this can only mean that the sonic longitudinal pulses generate transverse vibration at the muzzle, which I have observed using my limited accelerometer work.

 

[Kyle Schultz]

In the immortal words of Bill Parcells...

"Just show me the baby."

 

[CharlieNC]

In the immortal words of Bill Parcells...

"Just show me the baby."

I rather enjoy making the baby! To each his own....

 

[Dave M.]

When attempting to achieve the level of accuracy and precision required in Short Range Group and Score, seating depth is one of the most important aspects of a competitive tune.

This ^^^^ and you won’t likely find too many top level benchrest quality shooters that “jump” bullets.

 

[Dave M.]

As computational method vs target analysis:
Since there are many factors/contributors that all happening at the same time. The engineering solution is to model the system, rifle/load/shooter (or rifle supported by rest/mechanical recoiling machine) and then study the contribution of each factor to the outcome (accuracy at the target).

Al Varmint: Studied barrel harmonics using FEA and did POA vs POI analysis
Long: Studied barrel dilation/contraction due to powder explosion vs radial dispersion of the bullet

I also studied the Barrel dilation/contraction "nodes" along the barrel and its influence on MV SD. More specifically, by studying the derivative of the bullet acceleration along its path in the barrel

Off topic and not what the OP implied or I believe was intending for the readers to gain from reading it. Your use of the word node is completely different than what gunsandgunsmithing was attempting to convey to you.

 

[Dave M.]

I love this stuff! Ultimately, knowing how to use a tuner to manipulate tune to our benefit is way easier than knowing how or why they do it, to most people. Understanding it better may help but frankly, using one is easy and as said above..the target is all that matters.

I love talking shop with you Mike. Even though I’m an engineer, you bring out even more “engineer” inside of me. Lol. Look forward to chatting with you tomorrow.
Dave M.

 

[JEFFPPC]

So easy but many find a way to make it hard.