Data gathering for barrel design theory
- Thread starter darkangel_r2
- Start date
Here is a picture to help you visualize what I am talking about. I want to create a calculator that can put any chambering and bullet combination on the highlighted side of the curve by changing barrel length and profile.
RegionRat
Gold $$ Contributor
You can try to estimate harmonics of bbl sections based on the dimensions and the materials. That is easy enough.
When things get difficult is when it gets to boundary values and damping.
How the bbl connects and what it connects to are very difficult to estimate and also very critical to extrapolating a trajectory out to the muzzle or beyond.
The OBT models that are just based on the speed of sound in steel, do not account for other structural dynamics, so when you see models that are only based on length you know what you have.
The individuals who have published their own bbl structural dynamic analysis were always resource limited. They did some amazing work for spending their own money.
I'm not trying to discourage you from trying, but don't be too surprised when the challenge becomes the resources needed to model and test those more complicated boundary issues or to get damping data.
There are many harmonics that line up with exit times. The problem is estimating which ones are significant enough to affect the trajectory, and those require expensive lab work and damping data.
When things get difficult is when it gets to boundary values and damping.
How the bbl connects and what it connects to are very difficult to estimate and also very critical to extrapolating a trajectory out to the muzzle or beyond.
The OBT models that are just based on the speed of sound in steel, do not account for other structural dynamics, so when you see models that are only based on length you know what you have.
The individuals who have published their own bbl structural dynamic analysis were always resource limited. They did some amazing work for spending their own money.
I'm not trying to discourage you from trying, but don't be too surprised when the challenge becomes the resources needed to model and test those more complicated boundary issues or to get damping data.
There are many harmonics that line up with exit times. The problem is estimating which ones are significant enough to affect the trajectory, and those require expensive lab work and damping data.
The BC’s and excitation combined with timing makes this a futile exercise. Think we are saying the same thing.
Thats the reason why I wanted the lowest order vibration mode to be "built into" the barrel design as higher order terms are easier to handle on the range. But the lowest order term often necessitates a barrel weight of sorts to align it correctly if the barrel is the wrong length/profile.
Yeah I know some OBT models are pretty hokey. If your only input is length I doubt that output is worth much. But the general idea of driving frequency vs response certainly explains a lot of phenomena that appear on paper. But one thing at a time. Another thread after this one produces what I need.
Crowd sourcing raw data and limiting your model to the lowest order term can cut though a lot of these issues. Quality worked examples have always been the key to understanding any dynamic system and that's why I am here as I only have so many guns.
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Can you elaborate? BC's? Excitation? Timing?
Boundary Conditions for the model. Excitation, what gets the vibration going and timing of that. Just eigen frequencies will not be of much value. A FEM code can produce a lot of numbers, but not always of value.
Because the trend I am hunting for is so general (is it going up, down, or staying flat as velocity increases) enough worked examples and a FEA of the lowest order vibration mode adjusted to fit raw data should suffice. That is why the goal for this calculator is extremely limited. Lowest order only no threads, tuners or breaks, and free floated.
In my opinion there are multiple false assumptions as the basis of this exercise
First: Basic projectile motion. More speed equals less drop from an initial horizontal vector. Period. There cannot be a consistent inverse correlation with speed. FEA uses the laws of physics, it won’t deny them. Any delta is user input error.
Second: A barrel does not resonate on a single plane under harmonic vibration. It may trend more to a single plane, but even that is debateable, considering empirical data on how groups tighten into a node. Even if so, you would need to ensure that each individual barrel can be accounted to “clock” correctly for a vertically biased dispersion. This will change headspace, barrel length, and exit timing, starting you over.
Third: Your stated goal seems to be in line with calculating the exit timing of the “trough” of a wave for subsequent pressure nodes. You are then trying to equate this to barrel dimensions, which are completely independent variables.
Have you ever taken any good training on the 5Why methodology? Aside from being a problem solving tool, it is also very useful as a prevention for jumping to conclusions. I worked for a Japanese design firm that used 5Why to develop DFMEAs, not just amend them. The only redesigns we ever saw was when customers needed a resulting change from mating parts. It applies to DOE the same way. Highly suggested.
First: Basic projectile motion. More speed equals less drop from an initial horizontal vector. Period. There cannot be a consistent inverse correlation with speed. FEA uses the laws of physics, it won’t deny them. Any delta is user input error.
Second: A barrel does not resonate on a single plane under harmonic vibration. It may trend more to a single plane, but even that is debateable, considering empirical data on how groups tighten into a node. Even if so, you would need to ensure that each individual barrel can be accounted to “clock” correctly for a vertically biased dispersion. This will change headspace, barrel length, and exit timing, starting you over.
Third: Your stated goal seems to be in line with calculating the exit timing of the “trough” of a wave for subsequent pressure nodes. You are then trying to equate this to barrel dimensions, which are completely independent variables.
Have you ever taken any good training on the 5Why methodology? Aside from being a problem solving tool, it is also very useful as a prevention for jumping to conclusions. I worked for a Japanese design firm that used 5Why to develop DFMEAs, not just amend them. The only redesigns we ever saw was when customers needed a resulting change from mating parts. It applies to DOE the same way. Highly suggested.
The single most valuable thing I can tell you in terms of trying to estimate what is happening is...gigo. Now, how do you distinguish garbage from the rest?.....testing!
Spend some time behind a gun rather than a keyboard and make both results agree. I did it so you can too..but ultimately, there are too many changing variables to calculate. You have to quantify first...then calculate based on those findings.
Illsay this and it might put it in better perspective for you.
Using my cf tuner, there is only about .004-.005 of tuner travel, between perfect tune to completely out of tune.
Ponder on that.
Edit...this is not a one off test, but over a few thousand different barrels using my tuner!!!! It's so predictable that I can tell you what your approximate barrel contour is, by a test target.
You're close, but you're barking up the wrong tree, still.
Spend some time behind a gun rather than a keyboard and make both results agree. I did it so you can too..but ultimately, there are too many changing variables to calculate. You have to quantify first...then calculate based on those findings.
Illsay this and it might put it in better perspective for you.
Using my cf tuner, there is only about .004-.005 of tuner travel, between perfect tune to completely out of tune.
Ponder on that.
Edit...this is not a one off test, but over a few thousand different barrels using my tuner!!!! It's so predictable that I can tell you what your approximate barrel contour is, by a test target.
You're close, but you're barking up the wrong tree, still.
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I know for a fact that barrel harmonics can change POI at 100 yards to a larger degree than a change in velocity. This is not likely the case at all distances with all barrel lengths/profiles. That is why I ask for distance the target was shot at as well as barrel length/ profile info.
Its pretty well accepted that vertical variation due to harmonics is significantly greater than horizontal. Cases where this is not true are likely cases that you mention the muzzle orientation is significantly off center and not in the vertical plane. I am unaware of the true magnitude of this effect in regards to lowest order harmonics in the 3,6,9, and 12 positions. I doubt the effects of improper indexing are large enough to kill a lowest order harmonic amplitude. Tuning frequency amplitudes would likely see it.
Not pressure nodes. Minimum vertical dispersion nodes. I want fast vertical harmonic node at the same level or below the slower (at close range). As stated above I know that can fall apart at long range depending on the velocity gap between vertical nodes.
I ran Kaizen and 6sigma programs for a foundry a few years back so I am familiar with the thought processes.
Long range load development at 100 yards.
I remember a photo where it looked as though David was going to crown Jeff Cochran.....
forum.accurateshooter.com
This thread has many examples of what I am describing.
RegionRat
Gold $$ Contributor
@darkangel_r2
I can see the forum is going to jump up and down on you for being inexperienced, and energetic. This is the new normal, so I hope you can get used to it.
There was a time when that was harnessed, corrected, and directed, rather than attacked. Those days are long gone.
Try and carry on with your efforts and take everything with a grain of salt.
The skeptics are not right or wrong, they are just pointing out the pitfalls of where you are headed because some of them have been down this road.
We are all rookies at some point. None of us are born into interior or exterior ballistics. There are some families that are invested in the topics and start their young into shooting early. When one of those folks takes an engineering path, they become dangerous.
Most are not involved in ballistic weapon systems design, physics or engineering. That doesn't mean they don't know what they are talking about when it comes to ballistics and shooting, but they may not speak your language and you don't speak theirs. Try and be diplomatic with your ideas. You need them more than they need you, so take it slow.
If you are interested in discussing or testing a theory, try and bring it on as a theory rather than a bold statement for example. You will attract less flak.
I am assuming you have the background to run FEM and dynamics of some sort and you should follow your interests. This forum is still one of the best places to learn and share your background, but you better learn to have a thick skin and take it slow till you get familiar with the exterior/interior ballistics and shooting experience.
Good luck with your efforts. I hope you stick with it and run it to ground.
I can see the forum is going to jump up and down on you for being inexperienced, and energetic. This is the new normal, so I hope you can get used to it.
There was a time when that was harnessed, corrected, and directed, rather than attacked. Those days are long gone.
Try and carry on with your efforts and take everything with a grain of salt.
The skeptics are not right or wrong, they are just pointing out the pitfalls of where you are headed because some of them have been down this road.
We are all rookies at some point. None of us are born into interior or exterior ballistics. There are some families that are invested in the topics and start their young into shooting early. When one of those folks takes an engineering path, they become dangerous.
Most are not involved in ballistic weapon systems design, physics or engineering. That doesn't mean they don't know what they are talking about when it comes to ballistics and shooting, but they may not speak your language and you don't speak theirs. Try and be diplomatic with your ideas. You need them more than they need you, so take it slow.
If you are interested in discussing or testing a theory, try and bring it on as a theory rather than a bold statement for example. You will attract less flak.
I am assuming you have the background to run FEM and dynamics of some sort and you should follow your interests. This forum is still one of the best places to learn and share your background, but you better learn to have a thick skin and take it slow till you get familiar with the exterior/interior ballistics and shooting experience.
Good luck with your efforts. I hope you stick with it and run it to ground.
I have a limited amount of guns. The quality ones already have full work ups done. That's why I want more data.
If I had 20 bench rest quality rigs I would not be making this thread. I do not. More shots down my guns in the same unthreaded configuration does me no good. I need more data samples to set parameter's for a calculation which I can then buy an experimental barrel to verify.
I know that. Eric Cortina has always said that tuning windows were aprox .006" wide with his tuner.
I want you to tell me what you think I am saying.
Hooo, boy! The major issue with this kind of simulation is that the math just isn’t accurate enough. Most properties are statistical averages. Individual billets (could even be bars, or sections of bars) have properties that vary “heat” to “heat”. (The aerospace guys track heat lots of materials.). This WILL affect the prediction. Also the reason property “values” are only valid to about 3 or 4 significant figures. Way too coarse for this as, it is my (semi-educated) guess this calculation requires these values to be at least 6 significant figures.
Barrel heat was one of my concerns and I almost made slow fire a criteria as a mediator.
Actually the graph above has the timing window on the order of 0.00035 seconds. Its a full 1/3 of the time a typical bullet is in the bore for a shot. Keeping it to the lowest order term present on the target should keep this calculation viable given enough examples of up and down trends.
RegionRat
Gold $$ Contributor
@riflewoman for most, we teach engineering by safe siding with a margin. That was for the average masses.
When the pencil was sharpened and we had the fast students, we taught them to understand the probability that anything they thought they knew was only a statistical probability.
To design something to withstand a load was one level of engineering. To your point, to design something to break within a command was another.... this required understanding that everything we think we know, is an illusion.
When the pencil was sharpened and we had the fast students, we taught them to understand the probability that anything they thought they knew was only a statistical probability.
To design something to withstand a load was one level of engineering. To your point, to design something to break within a command was another.... this required understanding that everything we think we know, is an illusion.
By “heat”, I’m referring to the melt lot of material. There is also the “heat treat” of the material, but that may not be a Factor.
There is also the issue that barrels vibrate in three (or more) axes. All of them affect the bullet. The math and the software isn’t there yet.
Correct, for close range. Velocity easily wins out on dispersion at longer ranges, which you have acknowledged.
Velocity is resultant of pressure for any given cartridge. You are looking for a lower POI for the subsequent higher velocity (pressure) flat spots, correct? This would mean exit timing on the lowest position of the muzzle during harmonic vibration, and an increase of amplitude of the wave. Since slower = drops more, a sufficient increase of downward angle is required to overcome the increased velocity.
I think you are mistaken on this aspect. The dispersion is all based on tune. Keep in mind that without an ES = 0, that velocity biases this some. States of tune can give many different shapes, influenced by both pressure and barrel harmonics. Vertical, horizontal, and diagonal stringing will often all be roughly the same length, end to end. These are all different states of tune.
I am not referring to improperly headspaced barrels. Because we do not see consistent stringing, but rather various patterns resulting from barrel harmonics, we must infer that the harmonic has a radial nature. This may be elliptical in shape, or something much more complex (Spirograph?). Using an ellipse as an example, there is a polar trend where you will see the tightest nodes, harmonically. That ellipse is not guaranteed to be vertically oriented. Therefore, clocking a barrel would orient the ellipse accordingly. I personally believe the harmonic motion to be much more complex, like polar coordinate shapes. This would explain the change in shape according to states of tune.
I would imagine that a good barrel maker would require material properties to be in pretty tight spec to accept a lot of stock. Same thing for heat treat and stress relief. These kind of variables are the one thing I am hesitant about.
Vaughn, kolbe, and Varmint AI all have FEA graphs fit to experimental data that seems to work well with the lowest observable vibration mode.
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
See vaughn chapter 4 worked example for a 270 win.
and varmint ai here.
I agree in general as its a self defeating system. A whippy barrel can have more vibration amplitude but its frequency and therefore difference in velocity is much larger between nodes thus giving the velocity separation the edge at long range. And stiff barrels don't have the vibration amplitude to make up their smaller difference of velocity between nodes. I wouldn't say easily and I'm sure there are exceptions but I would accept that statement as a general trend at range.
Anywhere on an upswing works. If the fastest bullet leaves at the exact bottom of a trough then all the slower bullets leave with more angle. Conversely if your slowest bullet leaves at the exact top of a peak then all bullet faster than that one will leave at a lower angle. And anywhere between these two conditions works.
Vaughn talks about it in his book. Don't remember the exact page but its in chapter 4. Check the link above this post for his book.
Neither was I. The bore is not strait so the bullet leaves at an angle relative to what would be the exact center of the muzzle face. Horizontal dispersion is exacerbated if this angle is in the horizontal plane and not the vertical.
I agree, the muzzle will travel in all 3 directions in a complex pattern. Most of these shapes or movement patterns are oriented in the vertical plain due to preloaded moment in the system due to gravity pulling on the free floating barrel. The higher the order of the vibration mode the lower the amplitude so for a stiff barrel there are probably only a few modes present with large enough amplitude to impact accuracy.
And lucky for us physics makes it so the barrel spends a disproportionate amount time in its maximally flexed peaks and troughs so we can try to line some of these up.
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