Data gathering for barrel design theory

[darkangel_r2]

Hello everyone,

I am gathering data to try to explain a certain phenomena. Why do some rifles center of groups trend down or up as velocity increases. The goal of this thread will be to develop a calculator that reliably calculates barrel length and profile required to produce a flat or general downward trend in group position as velocity increases.

In this thread I would like you to post your load development targets if you meet a few criteria listed below.

PLEASE READ THEM ALL BEFORE POSTING DATA

1. You know the dimensions of the barrel. Use format below in inches. (please include the chambering as well ex. 308 win, 6br, ect..)


Sporter and


2. The muzzle is unthreaded and no weights were attached to the barrel (THIS INCLUDES MAGNETOSPEEDS) This makes calculations much easier.

3. The scope is untouched while shooting groups. No adjustments to elevation or windage made between groups.

4. The barrel is completely free floating to the action/ recoil lug.

5. More than one shot per charge level.

6. Make sure you know what range the target was shot at.

7. Need to have bullet and powder used and powder charges listed.

8. Each group needs to be identifiable to correlate to a charge level.

9. Average velocity for each group or velocity for each individual shot in the group.

10. Barrel steel type. Stainless or chromoly

BONUS POINTS not needed but helpful.

1. If you have group center position relative to POA from on target or similar software.

2. Photo of the rifle in the configuration the load dev was run in.

3. Jump to lands to jam length for each group.

example:



Thanks guys.

 

[Homerange]

You need also factor in barrel steel type.

 

[darkangel_r2]

You need also factor in barrel steel type.

True will add that as a requirement.

 

[jackieschmidt]

Are you sure you are not starting at a false conclusion.

I have spent countless hours at the range with 6PPC’s, 30BR’s, 6BR’s and more, and any substantial increase in the charge results in the groups forming higher on the target, either at 100 or 200 yards.

I load at the range where results are instant, in the same conditions.

Now, if you are talking about small changes within the tune window, there is a possibility that the center of the group might be a little higher or lower due to the different barrel harmonics as a result of a slightly different charge.

As an example, if I am shooting my 6PPC in the upper load window at 30.2 grns of 133, and it is agging at about .280, and I go to 30.4 to tighten it up, the center of the group might be a tad different Either up or down.

However, if I am shooting in the lower window, at around 28.8 grns, and dice to go to 30.4, that group center is going up on the target.the reason is the increase in velocity influences the bullets drop greater than the change in barrel harmonics.

 

[darkangel_r2]

Are you sure you are not starting at a false conclusion.

Fairly certain. I know I have seen targets on here with a general downward trend with increasing velocity.

Long range load development at 100 yards.

Any takers on this grouping? 6.5 creedmoor ELD 140s Did 2 tests. 2nd test had some 5-10 mph wind which I tried waiting to subside each shot because it would move the target (on pvc stand)

forum.accurateshooter.com

not the best example since the accuracy is poor in general but its got a good number of shots per group.

I have spent countless hours at the range with 6PPC’s, 30BR’s, 6BR’s and more, and any substantial increase in the charge results in the groups forming higher on the target, either at 100 or 200 yards.

I load at the range where results are instant, in the same conditions.

Now, if you are talking about small changes within the tune window, there is a possibility that the center of the group might be a little higher or lower due to the different barrel harmonics as a result of a slightly different charge.

As an example, if I am shooting my 6PPC in the upper load window at 30.2 grns of 133, and it is agging at about .280, and I go to 30.4 to tighten it up, the center of the group might be a tad different Either up or down.

No I'm talking about a real general downward trend where the faster plateau is lower realative to POA than the slower plateau.

However, if I am shooting in the lower window, at around 28.8 grns, and dice to go to 30.4, that group center is going up on the target.the reason is the increase in velocity influences the bullets drop greater than the change in barrel harmonics.

I am sure this statement is true for extremely stiff barrel profiles. I do not agree that it is true for all lengths of all profiles.

I know for a fact that in a few of my own private examples that velocity alone should have made the shots rise by .24" but the shots actually went .85" high. So in some chambering with some profiles and length the harmonics can move bullets significantly more than velocity alone would.

 

[Homerange]

This may be an exercise in futility due to all the barrel steel types available:

AccuCaliber™ Gun Barrel Steels | Gerdau Website

www2.gerdau.com

 

[JimSC]

so how do you plan on accounting for two of the largest factors in the accuracy and precision. Environmental effects and the shooters skills. I would bet a fair sum that Erik Cortina, F Class John or Laurie Holland could swap gear with me and still produce smaller and more consistent shot groups than I could.

Not trying to disparage your plan but to do this study properly you would need a shooting tunnel and a machine rest

 

[darkangel_r2]

This may be an exercise in futility due to all the barrel steel types available:

AccuCaliber™ Gun Barrel Steels | Gerdau Website

www2.gerdau.com

Most mechanical properties are similar between the to eachother in each class. Common stainless steels used in rifle barrels have very similar properties. Same thing with chromoly.

I think the variance of mechanical properties between the two is more of a difference than the variance in properties for the types commonly used in each category.

 

[darkangel_r2]

so how do you plan on accounting for two of the largest factors in the accuracy and precision. Environmental effects and the shooters skills. I would bet a fair sum that Erik Cortina, F Class John or Laurie Holland could swap gear with me and still produce smaller and more consistent shot groups than I could.

Not trying to disparage your plan but to do this study properly you would need a shooting tunnel and a machine rest

I'm simply trying to find a way to get an unmodified barrel to trend flat or down with an increase in velocity. I'm not concerned with trying to predict accuracy or percision at this point.

Thats a load development and shooting skills topic. Neither of those are pertinent to this goal.

 

[tomswede]

You are wasting your time. This is impossible with an axisymmetric barrel profile. Probably with any profile.

 

[darkangel_r2]

You are wasting your time. This is impossible with an axisymmetric barrel profile. Probably with any profile.

I disagree. Finite element analysis can work fairly well for most barrel contours. I simply need real world data to tune the models.

 

[Dusty Stevens]

You are wasting your time. This is impossible with an axisymmetric barrel profile. Probably with any profile.

And some rules state barrel tapers so there is that

 

[gunsandgunsmithing]

I'm sorry but, do you think that you are the first one to think of all this?
You are NOT!

Why do you think its is that I didn't reply to your previous posts and messages? I did try to point you in the right direction...but you had your own opinion and your mind was set that everyone was wrong but you.

I've already done just about every test you propose and my results are posted...but your are either too hard headed or too lazy to look them up. You are not the first(nor am I) to research your direction. You can either do it for yourself or take previous work as viable..that's entirely up to you.

But just either test for yourself or shut the hell up! You are just clueless! I'm not saying you are not smart...but you are very much looking for answers without doing your own testing...while at the same time...arguing others test results. That just doesn't give you or your posts any credibility.

Again, I'm not questioning your intelligence...I do think you are a smart kid...But do some damned work before you question others WORK! And you still have know IDEA how much work I mean!!!

 

[Dusty Stevens]

I gotta wonder why it matters which direction it trends with a velocity change?

 

[JFrank]

To trend down or flat with an increase in powder and velocity ? Where I shoot the event is referred to as overlap, I see with OBT achieved the rounds impact that plane dispute a change in powder charge but until that point I have seen rounds impact in all directions.

 

[darkangel_r2]

I gotta wonder why it matters which direction it trends with a velocity change?

Higher velocity rounds impacting lower on the target should keep trajectories together better than the reverse condition. Its positive compensation but on a vibration mode lower in frequency than the ones typically tuned on.

 

[RegionRat]

Starting out with the background homework is always wise.
https://www.varmintal.com/aflut.htm
https://www.varmintal.com/a22lr.htm
https://www.varmintal.com/aeste.htm
https://www.varmintal.com/atune.htm
https://www.varmintal.com/apres.htm
Noodle around on his list, you will find many very good pages where he runs FEM on bbl dynamics and also runs field tests to check his trends and shares photos of the results.
You may find you don't need to repeat his work, or you may find a new hobby.

I'm in for the range reports.

 

[darkangel_r2]

.

Starting out with the background homework is always wise.
https://www.varmintal.com/aflut.htm
https://www.varmintal.com/a22lr.htm
https://www.varmintal.com/aeste.htm
https://www.varmintal.com/atune.htm
https://www.varmintal.com/apres.htm
Noodle around on his list, you will find many very good pages where he runs FEM on bbl dynamics and also runs field tests to check his trends and shares photos of the results.
You may find you don't need to repeat his work, or you may find a new hobby.

I'm in for the range reports.

I've read through the Varmint AI reports, Kolbe papers, Vaugh, and a good number of threads on here. What I am trying to do is build a calculator that will allow me to select a barrel length and profile that will place my exit time on the red outlined side of the curve. That is not the frequency we tune on, the small periodic saw teeth on the slope are what we normally tune on. It is a lower order vibration mode than that.

 

[tomswede]

I disagree. Finite element analysis can work fairly well for most barrel contours. I simply need real world data to tune the models.

Yes, and that’s where you will waste your time. Think about the basic problem and what you are solving for before starting to mesh

 

[darkangel_r2]

Why do you think its is that I didn't reply to your previous posts and messages? I did try to point you in the right direction...but you had your own opinion and your mind was set that everyone was wrong but you.

I don't recall where our opinions actually differed. You supplied me with Liljas stiffness calculator that I used to check my work. Thank you for that.

I've already done just about every test you propose and my results are posted...but your are either too hard headed or too lazy to look them up. You are not the first(nor am I) to research your direction. You can either do it for yourself or take previous work as viable..that's entirely up to you.

I looked around in the search function, I found a ton of posts from you on barrel tuners and some on harmonics but barrel design was pretty sparse. I may either be blind or its hiding deep in the search function but if you have posted a thread with information pertinent to this goal please send me a link.

But just either test for yourself or shut the hell up! You are just clueless! I'm not saying you are not smart...but you are very much looking for answers without doing your own testing...while at the same time...arguing others test results. That just doesn't give you or your posts any credibility

Again, I'm not questioning your intelligence...I do think you are a smart kid...But do some damned work before you question others WORK! And you still have know IDEA how much work I mean!!!

I don't have enough high quality rifles to fit a model to. I have 5 fully worked examples from rifles I think are high enough quality to represent the type of rifle the calculator is meant to build. I don't know what you are referring to as "other peoples work" that I have questioned in any manner polite or otherwise. If I have offended you in some way I want you to know that is not my intent.