Barrel Behaviour Theory

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williada
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Re: Barrel Behaviour Theory

#31 Postby williada » Tue Jun 05, 2018 11:15 am

John I may have confused you earlier on another thread when I commented Varmint AL was looking at two closed ends like a guitar string and not one closed one end and open at the other in a tube. I think I used the term open in Al's discussion as the mind was going faster than the fingers could type. I was thinking of the outcome which has not changed. Sorry. It just means how waves are formed in different places i.e. at the muzzle and therefore their application and may give the wrong impression to readers. Varmint Al was just trying to get the concept across with regard to similarities in a simple way with regard to standing waves. The differences I see are where the anti-nodes form and nodes form at the ends of the tube. On an open tube with both ends open, anti-nodes are formed at the ends.

Its all about whether a frequency terminates on a node or an anti-node at the muzzle. A single, closed end tube has standing waves terminating on an anti-node at the open end and a node at the closed end; whereas a medium with both ends closed terminates a wave on nodes like a guitar string. That is highly relevant to a bloop tube component of a variable tuner as it alters the medium (barrel) length so that vibrations can be selected to make the barrel vibrate in a certain way and that relates to barrel behaviour theory. In addition, the length of a bloop tube helps us determine where we want to terminate undesirable vibrations so they do not distort the muzzle shape. The other benefit is to add a variable component to the tuner by which we can alter the boundary of the medium of the barrel and therefore the frequencies at the higher end because they are smaller and easier to deal with.

Standing waves are the duck's nuts of what this tuning is about. By understanding where these waves terminate tells you where to tune. In the old days a suitable barrel length was chosen to do the same thing. But in reality the simple geometric measure of barrel length for these calculations has to be adjusted because the outside atmosphere is also a reflection point. Musical instruments do take this into account if they are one closed end tubes.

Its all about understanding the speed of sound through different mediums. We know the speed of sound alters with temperature and air density and we see that in our groups. But what I am interested in and described briefly before and I am sure Peter will take us, is looking at the transmission of sound and therefor vibration at the medium boundaries of the whole system such as the stock and setup which relates to macro flip induced by fundamental vibrations. I am interested in the complex vibration analysis of Fourier analyisis hopefully Peter produces as a saw tooth pattern.

The following site is great and simple.

https://www.khanacademy.org/science/ap- ... wavelength

https://www.khanacademy.org/science/ap- ... wavelength

https://www.khanacademy.org/science/ap- ... d-of-sound

https://www.khanacademy.org/science/ap- ... bes-part-1

https://www.khanacademy.org/science/ap- ... bes-part-2
Last edited by williada on Tue Jun 05, 2018 3:04 pm, edited 4 times in total.

!Peter!
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Re: Barrel Behaviour Theory

#32 Postby !Peter! » Tue Jun 05, 2018 11:55 am

williada, if I understand you correctly, you are saying that there are open tube harmonics occurring. Am I understanding you correctly?

I'm also not so sure that standing waves are completely set up before the bullet exits, but let's wait until I've finished putting the theory out there and then start the discussion on this.

And thanks for adding those videos.

To others, some of you may have noticed that the physics classroom also has a class on sound which builds upon the wave class.
http://www.physicsclassroom.com/class/sound

williada
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Re: Barrel Behaviour Theory

#33 Postby williada » Tue Jun 05, 2018 2:43 pm

Peter, my mind got ahead of my fingers doing the typing by looking at the similarities and differences and so I edited the previous post. There is the added complexity in the rifle barrel of the two closed ends one being the bolt face and the other being the base of the bullet as it moves forward. The Fourier analysis should prove interesting if all the variables can be accounted for. I really don't think the standing waves are fully set up either or are incomplete and can't explain why harmonic values of between 19 and 25 work seem to work with certainty. As I have indicated before, there is something incomplete in the basic approach but what I do seems to work in practice and aligns as a good measure of theories. So they are important. Suppose it depends on how deep in the mud we want to go. Understanding how sine waves work has been a basic way into finding out how things work to shrink groups. I think the reality of the atmospheric density as a reflection point which is mainly a function of temperature and humidity is more important than most think on the internal ballistics. Keeping records of this does assist with tuner settings and consequently barrel behaviour.

!Peter!
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Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#34 Postby !Peter! » Tue Jun 05, 2018 3:06 pm

Thanks for clarifying williada, I think there is going to be some good discussion once we move to applying the physics.

One of the things that I haven't nationalised yet is the Purdy Prx, hence the clarification. I posted here some time ago the physics (open tube harmonics) that it is claimed to be based on but I just don't see how that can occur in a barrel with a bullet exiting....

williada
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Re: Barrel Behaviour Theory

#35 Postby williada » Tue Jun 05, 2018 3:41 pm

Peter, I am about to head out the door. But the fact that Purdy uses the odd number harmonic values calculation means he can't be applying open tube harmonics but rather closed tube harmonics and I am thinking the difference in true values may be due to atmospheric reflection as the air pulse moves against the atmosphere so the geometric length can has to be be fudged compared to the true harmonic length where the node must form in the atmosphere forward of the barrel? Can't help but think there must be a formula for a reconstructed value that someone has done in another application because physics is physics. I've only got half a brain these days so I will leave that to you younger bright sparks or someone to comment with experience.

John T
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Location: Brisbane

Re: Barrel Behaviour Theory

#36 Postby John T » Tue Jun 05, 2018 4:09 pm

Williada, I have mistakenly assumed that the barrel is an open-end medium, without taking into account the BULLET.

Does this mean that the medium has a closed and stationary end and a closed but moving end?

If so, does this mean that new standing waves are being generated constantly as the bearing surface moves up the barrel, culminating in an antinode at the muzzle?

Like Tim, I have a headache.

Regards,
John Tracey.
5.6.18

GSells
Posts: 243
Joined: Sun Aug 13, 2017 11:04 pm

Re: Barrel Behaviour Theory

#37 Postby GSells » Tue Jun 05, 2018 8:08 pm

6AFB02C3-F36C-4207-8C21-CC41AE210D53.jpeg

Thought I would try a different approach!!
You do not have the required permissions to view the files attached to this post.

GSells
Posts: 243
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Re: Barrel Behaviour Theory

#38 Postby GSells » Tue Jun 05, 2018 8:23 pm

!Peter! wrote:
Bigtravoz wrote:In your moving graphic Peter you showed the blue line with peaks much higher than the main waves, this is in theory what using a tuner should be aiming to control, reducing the radical peaks, and potentially increasing or decreasing the frequency of the other waves thus reducing and or stabilising how large each oscillation is to make the outcome easier to read.

I think a better way of thinking about a tuner is that it can change the shape and timing of waves.
Bigtravoz wrote: Somewhat like the ferrite cored lump on various cables cables does to stabilise the frequency through it and stopping radical off frequency waves interfering with other equipment ( there’s a correct name for it that’s right on the tip of my tongue, wish my brain still worked like it did ten years ago, I swear I am getting early onset Alzheimer’s some days!)

Sort of. The ferrite lump put on cables is to remove the high frequency/ high voltage spikes that occur when switching DC like what happens in a switch mode power supply and variable speed drives.
Bigtravoz wrote:I wouldn’t be surprised if tight rubber o’rings and or a strategically placed magnet on a barrel would have similar effect

Calling GSells, Care to comment about your strategically placed tight o’ring? :lol: :lol:

Bigtravoz wrote: It is a topic that I find very interesting and plan to research in earnest over the next few years as I have the funds to be able to.

Likewise, I’ve got ideas for experiment setups to investigate this, but I just don’t have time.
John T wrote:Hello Peter.

At the risk of being charged with hypocrisy, I have to say that you need to move on, rapidly, to RIFLE Behaviour Theory, or risk losing your audience.

Why do you persist with standing wave theory when there is no standing wave in a free-end medium?

Regards,
John Tracey.
4.6.18

John,
I’m allowing time for people to digest this material and for me to write it.

If you don’t think a standing wave can occur in a free-end medium then you should re-look at the physics classroom.

These is already enough in this tread to start applying to a rifle system but there are few more key snippets of theory to know to get deep enough understanding.

!Peter!

So Much to say but not smart enough to say it lol!
What I will say with some of the graphs is !!! What if your put some vibration dampeners or orings in the middle of that lot ? I’ve often said that orings are very much like shock absorbers and maybe this in neo nandathal terms is how it should be thought of ! It totally changes the harmonics profile and as I’ve said before like , “ the taming of the shrew!”
I’ve had a lot of flack from my lovely Qld Shooting friends about orings on my scope . Reading in regards to stock vibrations.
Do u think that a big NF Comp scope which looks like a big tuning fork has any input ? Like it’s not a huge thing but it all adds up .

GSells
Posts: 243
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Re: Barrel Behaviour Theory

#39 Postby GSells » Tue Jun 05, 2018 8:41 pm

I found it , I’ll bare all !! This was written a while ago and is not very tech ! But here it is my little thesis on Barrel harmonics.
Which way to move the tuner , jumping , jamming , barrel timing and ocw:

First up a disclaimer: I have no accolades next to my name ! So take my theories as just that . They are just theories until proven!

Ok , when a tuner is installed, it is not much different than say a guitar.
In the way when you put your finger on the fret board and induce harmonics, you are modifying the frequency.

Tuners do the same thing ! Ok so I'm at a Queens and a cold front comes through! I can feel the load go off slightly as the rounds are now do 15 fps .
Which way to move it ? Well to modify the mode 2 and mode 1 harmonies. One would hope to slow done the vibrations. So moving the tuner forward a couple of notches would in theory would bring it back into tune. This would have to be something that it practiced at club level by deliberate down loading by
.1-.2 gr and chronied to see what a couple of notches longer would yield ?
That is why I stick to mass dampers ! As I would be under pressure, stuff it up and spin the tuner the wrong way and may even induce negative compensation! Ouch if that is at a Queens !
They are idiot proof ! But not perfect !

Jumping , jamming is not all that different to adjusting the timing on an engine ! Let's say for arguments sake 7.5 thou is top dead centre or neutral tune ! 10 thou or more is retarding the barrel harmonics timing and 7.5 or jamming is advancing barrel timing.

When the primer is struck , this the first hint of vibration that is sent down the guitar like barrel! Then the charge goes off thus sending a donut like harmonics down the barrel all the way to the muzzle , then torque harmonics happen as the pill starts to spin , mode 2 vibrations start going to the muzzle and back again , then mode 1 Barrel whip starts of . By fine tuning with seat depth, you are hoping that you can intersect the whole symphony of vibrations and get the bullet to exit at the perfect timing or tune . Hopefully slightly positive compensating .

Yes it's possible to shoot great groops at 500 yds but at 1000 it's just crap . Optimum charge weight is another important aspect!
I will add that you can have ocw and obt perfect and still fall over at 1000 as it goes into a dead speed zone .
A zone that wind Sheer and chopping conditions induce yaw and variable BC and thus vertical ! Not to mention 10-4 slope or aerodynamic jump!



I'm quite open to scrutiny and friendly debate as this is where we all learn !
All of the above has come from learning in forums and brilliant minds like David Williams ( willaida ) .

Well that was a long time I wrote that , but I’ll put out there ! I’ll get ready for the incoming lol! :shock:

!Peter!
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Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#40 Postby !Peter! » Tue Jun 05, 2018 10:59 pm

GSells,
Thanks for putting it out there =D>

I think a better analogy to use is a garden hose rather than guitar string as a garden hose is more representative of a barrel.

Here's my thoughts on how the mid barrel O-rings work:

Let's assume that only the 1st, 2nd and 4th harmonic are present. The resulting wave would look like this:
Image

If the tuner is placed at 0.5 then it is at the anti-node for the 1st harmonic and node for 2nd & 4th harmonics. The effect of this is that the 1st harmonic's energy would be absorbed the most thus reducing its amplitude, while very little energy from the 2nd & 4th harmonics.

Here is what the resulting wave would look like if the 1st harmonic's amplitude was halved.
Image

If the tuner is placed at 0.75 then it is midway between the node and anti-node for the 1st harmonic, anti-node for the 2nd harmonic and node for the 4th harmonic. In this case the, not as much energy as before will be absorbed from the 1st harmonic, and the 2nd harmonic's energy will now be absorbed while very little energy from the 4th harmonics.

Here is what the resulting wave would look like if the 1st harmonic's amplitude was reduced by 3/4 and the 2nd harmonic's amplitude was halved.
Image

HOWEVER, this is assuming that harmonics are full established before the bullet exits.

!Peter!
Posts: 84
Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#41 Postby !Peter! » Tue Jun 05, 2018 11:02 pm

Also for everyone, I edited post #16 because I found an error in the Fast Fourier Transform. It doesn't change the points or discussion, just the picture looks better.

williada
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Re: Barrel Behaviour Theory

#42 Postby williada » Tue Jun 05, 2018 11:55 pm

John, there is a nightmare of different vibrations patterns to get your head around as we try to identify their sources, then try to work out how they mesh or interact and a lot of blokes who are specialists in this field know more than me. Yes, seeing some of those changing sections induced from the second major point of inertia with the bullet moving forward can be seen as closed and open section influences. Edit. that means there is another harmonic interaction of closed/closed end section behind the pill operating like an Hawaiian guitar lowering frequencies as the bullet moves forward and closed/open section in front raising frequencies still ending in an anti-node. The interference pattern of multiple sources of vibration won't be as simple as the introductory model of a sine wave pattern which gives people an idea of where best groups form. Where this may be going is trying to map and predict theoretically the vibration patterns I see visually in groups with a charge test which is set up under strict conditions of testing procedure.

Lets look at a couple of the impacts which I am sure Peter can help us refine. Imagine a bottle filling with water for the top section. Ever noticed as it fills up the pitch gets higher. This is because the sound gets reflected from the rising water acting as a moving, closed end apparatus. The frequency rises. This is separate from high frequency muzzle exit of the bullet but the frequencies all mix. Perce Pavy always said it was all in the last six inches. That's why these higher muzzle end frequencies are important to me. If we can manipulate them we can produce hummer groups. I don't think the lower frequencies do much damage or distortion at the muzzle as they are largely incomplete. So my goals are, to move high frequencies to where they don't matter in layman's terms or to reduce them or convert them into another frequency by changing their angle at the boundary of the medium. We need a minimum muzzle size at bullet exit.

I have used a back bore reamer for about thirty years which was tapered for TR barrels. Now to the casual machinist they might think it is easy to extract from the job. But to me I thought that a belled muzzle past the crown actually changed the high frequency to lower ones where there is less tendency to distort the muzzle by reflection. The length of of the back bore I believe is related to a node forward of the muzzle acting as a reflection point in the atmosphere. Air molecules get sucked in and out by pulse to form a standing wave but the outside air mass must add to reflected frequencies to lower the frequency too. Other scientists have also documented the bullet speeds up a little past the muzzle exit. Something is happening here in an unstable zone? Our simple sine wave tells us groups form well at the anti node on the muzzle. If a significant energy wave is moving in and out with changes in atmospheric density pressing back on the node to shove the energy back down the hole like putting your finger over a hose to stop it or allowing it to breath out further when the pressure is off then we can expect the group to change. This is where I think the musical theory of strict harmonics cause me to fudge their figures. The paper always tells the story. But I believe an acoustic end can mitigate and filter frequencies by lowering their value and damage at the muzzle as a way stabilizing the node outside the crown. I hope Peter can shed some light on this as I have only got best fit with just a bloop tube length. When I added a thimble to the tuner, I was able to manage the variability in reflection and link movements to group shape and conditions. I might be barking up a gum tree, but it works. It was trial and error refining this with the boring bar in later years on FO barrels. Again I was convinced the lowered frequency did not distort the barrel, it was the high frequencies. While a slow burning powder can reduce frequency it still burns further up to the tube hindering the damping process but you can still find ebbs between the spikes looking at paper. I look for the optimal timing. I think I found a more efficient way and I was tipped off by OCW theory.

With regards the breech end, I noticed with faster burning powders burning completely, (assisted by jamming them or changing leade angle) performed better even to the extent there was a significant air gap. I have traditionally used 100% powder density to achieve a better burn. A full burn is the secret. I asked myself why did fast burning powder with a large air gap giving wider velocity spreads still perform? Sometimes we can rightly assume the air /fuel mixture is right. But I feel there is more to it. So I refined the work after reading OCW theory to believe that what ever got the pill out before the first large pulse of lower frequency was reflected back from the first major inertia point of ignition, the projectile was subject to less interference and beat some trashing by getting the timing right. I also knew the higher frequency of the faster burning powder was easier to control at the muzzle than the relatively slower burning powders. Now velocity can move around - it does not seem to matter as much if we can get damaging high frequency out of the way. Higher frequency of fast burning powders also has more time to dampen with the peak pressure closer to the breech. Its still a bit of trial and error given so many competing ends hence the importance of the Fourier analysis. The other bonus maybe producing more lift for positive compensation by working with the low frequency vibration which does not fully complete and in my view does not significantly distort the muzzle but effects general lift angle. A correct balance may neutralize negative barrel lift with proper Fourier analysis. There are just so many options to test. To me chamber design has also to be another balancing component in volume terms in relation to harmonic lengths and bore size. That's another topic.

Graham, I just love your theories because sometimes there is a gem which connects to something else. There is an old Aussie in one of our clubs who shall remain nameless reckons in his youth he could fit 7 donuts on his mutton gun. Don't know how many sheep he killed?!! I never discourage people thinking. Its about observation and sometimes other people's thoughts help with an idea when trying to connect the dots myself. Never fear failure. Those that do can never achieve. But may I point out Graham that because there are different sources of vibration where each have their own harmonic frequencies you might have to brush up a tad with terminology when interpreting some of my stuff. One day I will have an opportunity to work with you because you are one hell of a trigger puller. Each bell is rung by a different hammer to generate a new shape.

I am looking forward to Peter's work and I am sure I will learn something too, as the quest is never over.
Last edited by williada on Wed Jun 06, 2018 11:05 pm, edited 2 times in total.

!Peter!
Posts: 84
Joined: Sun Oct 30, 2016 6:35 am

Re: Barrel Behaviour Theory

#43 Postby !Peter! » Wed Jun 06, 2018 12:52 am

williada, I hardly call what I'm doing here work. All I've done is to have spent the time to look at the work people have done before me and connect the dots with fundmental physics. The physics talked about here isn't new either as it hasn't changed since the middle of the 1700's.

It is those people who have spent the time to do detailed tests that have done the real work. Even Calfree deserves credit despite his patronising communication style and explanations that defy the law of physics.

GSells
Posts: 243
Joined: Sun Aug 13, 2017 11:04 pm

Re: Barrel Behaviour Theory

#44 Postby GSells » Wed Jun 06, 2018 6:49 am

Thanks Peter for your analysis on orings , I get the gist of your diagrams.

GSells
Posts: 243
Joined: Sun Aug 13, 2017 11:04 pm

Re: Barrel Behaviour Theory

#45 Postby GSells » Wed Jun 06, 2018 10:46 am

williada wrote:John, there is a nightmare of different vibrations patterns to get your head around as we try to identify their sources, then try to work out how they mesh or interact and a lot of blokes who are specialists in this field know more than me. Yes, seeing some of those changing sections induced from the second major point of inertia with the bullet moving forward can be seen as closed and open section influences.

Lets look at a couple of the impacts which I am sure Peter can help us refine. Imagine a bottle filling with water for the top section. Ever noticed as it fills up the pitch gets higher. This is because the sound gets reflected from the rising water acting as a moving, closed end apparatus. The frequency rises. This is separate from high frequency muzzle exit of the bullet but the frequencies all mix. Perce Pavy always said it was all in the last six inches. That's why these higher muzzle end frequencies are important to me. If we can manipulate them we can produce hummer groups. I don't think the lower frequencies do much damage or distortion at the muzzle as they are largely incomplete. So my goals are, to move high frequencies to where they don't matter in layman's terms or to reduce them or convert them into another frequency. We need a minimum muzzle size at bullet exit.

I have used a back bore reamer for about thirty years which was tapered for TR barrels. Now to the casual machinist they might think it is easy to extract from the job. But to me I thought that a belled muzzle past the crown actually changed the high frequency to lower ones where there is less tendency to distort the muzzle. The length of which has to be related to a node forward of the muzzle acting as a reflection point in the atmosphere. Other scientists have also documented the bullet speeds up a little past the muzzle exit. Something is happening here? I hope Peter can shed some light on this. I might be barking up a gum tree. It was trial and error refining this with the boring bar in later years on FO barrels. Again I was convinced the lowered frequency did not distort the barrel, it was the high frequencies. While a slow burning powder can reduce frequency it still burns further up to the tube hindering the damping process. I look for the optimal timing. I think I found a more efficient way and I was tipped off by OCW theory.

With regards the breech end, I noticed with faster burning powders burning completely, (assisted by jamming them or changing leade angle) performed better even to the extent there was a significant air gap. I have traditionally used 100% powder density to achieve a better burn. I asked myself why did fast burning powder with a large air gap giving wider velocity spreads still perform? Sometimes we can rightly assume the air /fuel mixture is right. But I feel there is more to it. So I refined the work after reading OCW theory to believe that what ever got the pill out before the first large pulse of lower frequency was reflected back from the first major inertia point of ignition, the projectile was subject to less interference and beat the trashing by getting the timing right. I also knew the higher frequency of the faster burning powder was easier to control at the muzzle than the relatively slower burning powders. Now velocity can move around - it does not seem to matter as much if we can get damaging high frequency out of the way. Higher frequency of fast burning powders also has more time to dampen with the peak pressure closer to the breech. Its still a bit of trial and error given so many competing ends hence the importance of the Fourier analysis. The other bonus maybe producing more lift for positive compensation by working with the low frequency vibration which does not fully complete and in my view does not significantly distort the muzzle. A correct balance may neutralize negative barrel lift with proper Fourier analysis. There are just so many options to test.

Graham, I just love your theories because sometimes there is a gem which connects to something else. There is an old Aussie in one of our clubs who shall remain nameless reckons in his youth he could fit 7 donuts on his mutton gun. Don't know how many sheep he killed?!! I never discourage people thinking. Its about observation and sometimes other people's thoughts help with an idea when trying to connect the dots myself. Never fear failure. Those that do can never achieve. But may I point out Graham that because there are different sources of vibration where each have their own harmonic frequencies you might have to brush up a tad with terminology when interpreting some of my stuff. One day I will have an opportunity to work with you because you are one hell of a trigger puller. Each bell is rung by a different hammer to generate a new shape.

I am looking forward to Peter's work and I am sure I will learn something too, as the quest is never over.

Thanks David for the kind words , I’ll keep on learning .
It’s funny how you say the last 6” of the muzzle as this is where I’ve shoved the pink cricket handle grip rubber on my bart .284 ( smithed by Fairbarn) . And also where I say secondary orings should be placed . I would love to spill the beans on how to tune the barrel with orings . But again I’m sure people who have the passion will work it out ! It’s been very interesting read and my head hurts too!
Some of it goes way over it lol! I’ll try and stay out of Peter’s thread and let The people who know contribute!

Again very interesting thread !


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