Testing new discovery

[rsterne]

ahhhhhhh, well then forget about my POI comments.... *eyeroll*….

Bob

[robertr]

 No sweat Bob.

[darkcharisma]

<sub>"yeah Mike, why the heck did you not tell us that this is for bench rest only? i am a hunter dang it! "

"oh yeah, thanks for the secret to this device but i am not as appreciative as others "</sub>

=============

Hey Don, i love talking in third person perspective. i get to exaggerate a point and hopefully someone gets it. ya gotta get out of ya own shoes sometimes

the way i see it, hunting, target and bench shooting can be applied with this device. i can sit and hunt just like bench shooting. i can carry the weight cause i bench press 50lbs, i mean 250lbs...  whats the extra pound gonna hurt?

[KnifeMaker]

Allen, it is much appreciated Sir!


Denis, I glad you will not be offended if your device it tinkered with.


It did not work for the bullets. I think my barrel double wrapped with carbon fiber is too stiff for the light weight. I am looking for a lighter oil and gong to replace the (what looks like #( steel shot) with probably # 6 or # 8 birdshot. and test again.


With the short, light design, it would be fantastic for hunting in the woods.


One odd thing I noticed, not being able to attach an ldc to it, is the report. I dont' shoot the RS without one as I have hearing damage and it actually causes pain. However, somehow, it lessened the report or changed the frequency of the report. It is actually pleasant. Perhaps it acting like a longer barrel? I don't know.


If I don't have a lighter oil on hand, I will try distilled water Not something I would want to do permanently, but it shouldn't cause any issues short term testing.


I would very much lie to see the device to be able to perform in the actual off hand  hunting arena.  


Taso, Mr. Bob, Denis, Don, Duy, Travis and many  others, thank you for your efforts. A combo has to be found for each and every system. The more testing, the better to get this ironed out!


Every device will not work on every AG. Just as every pellet or bullet will not. The balance has to be found, like just about everything in shooting for accuracy. And the quest continues.  [size=78%]  [/size]


Mike

[Lefusil]

So I just finished reading all the way through this fascinating thread.
First, I think Mike handled this in a classy way.  Sharing it with the forum was both generous and smart.
I am eager to try it out.

FWIW- A couple things about vibrations and damping theory from engineering school.  Dampers work by dissipating energy, in this case the energy of the barrel motion is absorbed by the damping material (oil, powder, mercury).  Actually, it is really converting the energy from kinetic (motion) to heat.  Each shot heats the fluid up a little bit.  The addition of a MAD device will add both mass, and damping to the system.  So the mass is changing the mode and frequency of vibration (barrel tunner effect), and the damping fluid is attenuating the vibrations.  Viscous damping is typically modeled as being proportional to the velocity of the motion and resisting the motion's direction.   When you change the oil's viscosity, or the shot size, you are changing the damping forces on the barrel.  When you shift the location of the device, you are changing frequencies and modes of vibration, which also can change the effectiveness of the damping force.

I don't know how long the pellet is in the barrel of a typical air gun, but I know it is longer than a powder burner.  I expect the reason this work so well is because the air gun takes longer to push the projectile out of the barrel.  It is a VERY complex subject, with a lot of dependencies and the modeling of it  usually best done using numerical methods (as in the Varmint AL link Mr. Sterne posted, which was very good btw).  Trial and error is probably the fastest way to find a solution for a particular gun.

[darkcharisma]

When you change the oil's viscosity, or the shot size, you are changing the damping forces on the barrel.  When you shift the location of the device, you are changing frequencies and modes of vibration, which also can change the effectiveness of the damping force.

this is a simple explanation but it gives some insight into how it works. i know you mentioned trial and error is best. but is there actually some mathematical solution to this to determine the best weight NOT based on caliber but FPE? you know the feeling even if the current device works, but what if its not the best and requires more T&E.

[rsterne]

At 900 fps, the pellet is in the barrel about 3 mSec. (0.003 sec)…. However, it travels the last 1" in about 0.1 mSec. (0.0001 sec), and the direction that last inch is pointing determines the departure angle of the pellet.... For a pellet to hit 2" different POI at 50 yards, the muzzle departure angle is changing only 4 MOA (assuming that is the only reason for the POI change)…. I think that means that angle change must be occurring in 0.0001 sec....

I would suggest that the disturbing force causing the barrel to vibrate is likely somewhat proportional to the energy input (the FPE)…. but that is resisted by the barrel mass (so the heavier the barrel + damper the less amplitude)…. However, the frequency and amplitude will be somewhat inversely proportional to the barrel stiffness.... In other words, 10 times the FPE in a barrel that is 10 times as stiff may have a similar amplitude, but assuming the same length, the stiffer barrel would have a higher frequency.... I certainly do not have the brain power to contemplate such calculations....

Bob

[Lefusil]

When you change the oil's viscosity, or the shot size, you are changing the damping forces on the barrel.  When you shift the location of the device, you are changing frequencies and modes of vibration, which also can change the effectiveness of the damping force.

this is a simple explanation but it gives some insight into how it works. i know you mentioned trial and error is best. but is there actually some mathematical solution to this to determine the best weight NOT based on caliber but FPE? you know the feeling even if the current device works, but what if its not the best and requires more T&E.

I'm sure there is a mathematical solution, but probably too complex for a closed form solution (i.e. something you can plug FPE into and out pops the right damper parameters).  If you could figure even part of it out, i am sure you could earn a PhD.   One way to solve a problem this complex is to use a numerical method known as Finite element analysis, this breaks the big complex problem into a bunch of smaller less complex problems.  The link Bob posted to Varmint Al's analysis of his rifle is an example of this.

[Lefusil]

At 900 fps, the pellet is in the barrel about 3 mSec. (0.003 sec)…. However, it travels the last 1" in about 0.1 mSec. (0.0001 sec), and the direction that last inch is pointing determines the departure angle of the pellet.... For a pellet to hit 2" different POI at 50 yards, the muzzle departure angle is changing only 4 MOA (assuming that is the only reason for the POI change)…. I think that means that angle change must be occurring in 0.0001 sec....

I would suggest that the disturbing force causing the barrel to vibrate is likely somewhat proportional to the energy input (the FPE)…. but that is resisted by the barrel mass (so the heavier the barrel + damper the less amplitude)…. However, the frequency and amplitude will be somewhat inversely proportional to the barrel stiffness.... In other words, 10 times the FPE in a barrel that is 10 times as stiff may have a similar amplitude, but assuming the same length, the stiffer barrel would have a higher frequency.... I certainly do not have the brain power to contemplate such calculations....

Bob

Yep I agree.  The input energy is stored in the pressurized plenum (for a reg'd PCP), and it is released into the system and converted to motion.  Mostly of the projectile (good), and partially into deflecting the barrel (what we're trying to control).  Some is converted to heat, bullet friction with the rifling, and the internal damping present in the barrel material. 
I also agree about the stiffness.  The natural frequency of a spring mass damper system is proportional to the square root of the stiffness, and inversely proportional to the square root of the mass.  So a more massive barrel should have a lower natural frequency than a lighter barrel if they have the same stiffness.  In practice it is hard to change stiffness without affecting the mass.
The important part I think is knowing what part of the transient event we should be worried about.  Natural frequency is only really seen after the projectile has left the barrel in a PB.  While its traveling down the bbl it, and the pressure behind it are forcing a displacement in the bbl.  I thought the most interesting part of Varmint AL's was:

"POSSIBLY MODE SHAPES ARE NOT SO IMPORTANT.... I ran some FEA calculations of how a barrel reacted to the high gas pressure and recoil. The forced deformations from the high pressure gas and recoil cause the muzzle to change where it is pointing at the target when the bullet exits the muzzlet."

Not exactly sure what a "muzzlet" is (a smaller than normal muzzle?  ).  Kidding aside,  I thought it was interesting.  I guess real goal is to have the bullet / pellet leave the muzzle with it pointing in the same place each shot.  Since as the power of the energy release increases to get a heavier bullet flying, the forces involved increase too, and deflect the bbl more. The damper will resist the deflections that scatter the shots, and the groups tighten up.     It was actually pretty intuitive of Mike to stick one of these on the end of his bbl.  Kudos to him.

[Nvreloader]

And to go along with Bob's info and these last couple of posts,
 
Here is more info about the Harmonic Resonance Theory of barrels,
even thou this info is related to PB, I would believe that the same info would work for our air rifles,
I know that this info works with PB Bbl's and Quickload program.

http://www.the-long-family.com/OBT_paper.htm

This paper has some very good info, well worth reading, IMHO,

BUT, how can it be used for airguns, is the question?

Tia,
Don

[darkcharisma]

well now, it sounds to me like we have the recipe but no one knows when to throw them in the pot. even if we have parts of the recipe it will turn out something if we just throw it in the pot.

let me break it down and maybe we can work from there. no Phd required, i am not qualified but having a little Magnetic resonance education, i 'd like to "take a crack at it" as Texans here like to say.

Lets define the problem. the problem is clearly the barrel vibration. this can be minimized with a secured barrel band at the very end of the barrel or having some dampening or harmonic balancers in place. and since we are building a dampening system, we want to find the ideal weight and fine tune it later. this is the reason we are pursuing a mathematical equation. even though we have some data and can do trial and error but we want a good starting point.

lets convert all calibers into FPE and say that an airgun at 100fpe is able to vibrate the barrel at a constant frequency and amplitude and that An unknown weight can counter. now were just need to put it into an equation and work it out. for example, we know 14oz works for 95-100fpe from Knife's report. what was his frequency and amplitude? is 14oz the best weight or will 10oz be best?

forget every other detail like angle of exit and such. those will be solved when the barrel doesn't flex as much by having a clamp or a device capable of doing such.

well, can we all brainstorm a little and come up with an equation? i think we also need a man who has the equipment to measure the frequency and amplitude.

[rsterne]

say that an airgun at 100fpe is able to vibrate the barrel at a constant frequency and amplitude

This is a completely flawed assumption, IMO, because you are ignoring the stiffness and length of the barrel.... There are so many variables here that trying to use just one (FPE) in an equation will be doomed to failure.... Again, JMO....

Bob

[grand-galop]

well now, it sounds to me like we have the recipe but no one knows when to throw them in the pot. even if we have parts of the recipe it will turn out something if we just throw it in the pot.

let me break it down and maybe we can work from there. no Phd required, i am not qualified but having a little Magnetic resonance education, i 'd like to "take a crack at it" as Texans here like to say.

Lets define the problem. the problem is clearly the barrel vibration. this can be minimized with a secured barrel band at the very end of the barrel or having some dampening or harmonic balancers in place. and since we are building a dampening system, we want to find the ideal weight and fine tune it later. this is the reason we are pursuing a mathematical equation. even though we have some data and can do trial and error but we want a good starting point.

lets convert all calibers into FPE and say that an airgun at 100fpe is able to vibrate the barrel at a constant frequency and amplitude and that An unknown weight can counter. now were just need to put it into an equation and work it out. for example, we know 14oz works for 95-100fpe from Knife's report. what was his frequency and amplitude? is 14oz the best weight or will 10oz be best?

forget every other detail like angle of exit and such. those will be solved when the barrel doesn't flex as much by having a clamp or a device capable of doing such.

well, can we all brainstorm a little and come up with an equation? i think we also need a man who has the equipment to measure the frequency and amplitude.

If we assume what Rick is QUANTIFIED and could be validate would be a good start

I have taught a way that COULD WORK if we can ASSUMING that FPE  would be consolidated with the equal resistance of barel stiffness..

If other could confirm that, then, you could calculate the last 1/4 of the barrel length  the weight to be STABILIZE..

IF THE last quarter length weight is ( example of 4.7 grams) then the device would be the equivalent to ABSORB THE VIBRATIONS.

THAT could be a a start to have a constant  in the equation..

My 2 cents

[darkcharisma]

hey bob, i wasnt assuming this can be base on one simple equation. i was aiming to see if we all can come up with one to start and from there we convert it home with as many equations as needed, its a road map. and we are brainstorming...not assuming. all invalid ideas need be scrapped or put aside once verified not applicable.

well then, lets throw stiffness into the equation and of course frequency and vibration depends on the medium too. and stiffness can be closely related to hardness. why don't we take another crack at it and not give up by thinking there are too many variables? or its too complex? it may take us several "cracks" or hundreds, but never give up so easily...the pot is burning for the recipe...

Alain, Rich doesnt need to be validated...if he says he took some ed, then he did. just like me i took MRI course and certified but my knowledge is very limited to the human hydrogen interaction to frequency and amplitude of the magnetic gradients.

can someone throw Alain's ideas together with some equations too? the "weight" may need to be another equation alone once we find frequency and amplitude.

btw...length of barrel is already converted into FPE? Bob, dont hesitate to throw out something...i know you have at least tried and stopped somewhere...one equation at a time brother!

[grand-galop]

What I consider a baseline is when the barrel becoming so short that the device will not any longer be effective.
With a proposed length of barrel, in proportion, the FPE  will increase as the frequencies...
 From what I UNDERSTAND, THE NODE  will will come closer to the end of the barrel as the speed increase.

One thing that is not constant is the material used and the building techniques..
If a barrel TENSIONER is used in the build, I don't see why the device would be needed..
The material used I am talking here the LENGTH  AND THICKNESS..

[Nvreloader]

Duy

Have you read the Long info, from post # 489,
Chris long has already did this type of info for PB, but since they operate at higher psi than air rifles,
it's going to take some brain power to convert to our usage.

He list a computer function called MetLab for his work, which is above my pay grade............

The one thing I do know is, his OBT work does work with Quickload program,
but will not work with AG's, as I have found out etc.

Tia,
Don

[rsterne]

As I see it, here are some of the variables....

Variables affecting the force, acceleration and vibration generated:
FPE (further broken down into)
Bullet weight
Rifle weight
Velocity (critical in determining when the bullet arrives at the muzzle, relative to node location)
In addition, possibly air pressure and dwell (how they effect the vibration and bullet arrival time at the muzzle)

Variables affecting the frequencies and modes of vibration of the barrel:
Barrel OD (stiffness varies with the 4th power)
Caliber (larger bore reduces stiffness)
Barrel Length (longer reduces stiffness)
Material (ie how the dimensions relate to the stiffness)
Barrel Supports (ie free floating, or bands and where positioned)
Direction (plane) of primary barrel vibration (ideally should be vertical)

Variables affecting how the Damper/Tuner interacts with the node location and amplitude of muzzle movement:
Mass of Damper/Tuner (increased mass decreases amplitude and frequency, and decreases horizontal movement)
Position of Damper/Tuner (lengthwise and radially)

Variables affecting the damping effect of the material inside the Damper:
Damping Material (Mercury, Lead shot, powders, fluids, masses on springs, etc.)
Shot/particle size
Fluid viscosity (if any)
Fill ratio of Damper
Internal Shape of Damper
Mounting Position
Any use of springs (mechanical or magnetic)
Mounting method (ie solidly, rubber, etc.)

While it is possible to look at these items one at a time, to a large degree they interact, and changing one thing affects one or more of the others.... I have neither the brain power, or the computer power, to even try and sort through predicting how a given damper/tuner will work on a given rifle/pellet combination.... If you do, then more power to you.... If you don't, then jump in there, build something, and try something to increase our database of knowledge.... 

Having said that, I believe that more powerful PCPs may require a larger damping mass.... and the more flexible the barrel, the more effective the damper may be....

Bob

[oldpro]

 I believe Ive come up with a way to make a unit that should work with any power plant I talked with Michael about it in detail and will start construction as soon as I can, it will be somewhat elaborate to produce so give me some time but i think it should work with about anything its attached to.

[Taso1000]

Mr. Sterne,

I had a minor in math when I graduated college but haven't used any of it in 16 years.

I just saw that solving the problem has way too many components to try to represent and put into an equation.  Once you start adding shrouds, barrel bands, ldc's and our experimental damper, how do those fit in?  It's a rhetorical question, no answer necessary.   

I can see as adding every add on as mass, but I think they have more effect than that.  A barrel band would add mass and it's point of contact on the barrel has an effect on the barrel harmonics.  How is that represented mathematically?

Like I've said before, I wish I had taken more physics!   

Maybe these other interactions, besides the mass, have very little effect that they can be disregarded?  My brain is wired to say no to that question.  lol

I haven't looked in a couple days, but when I did I couldn't find a general conclusion online on how our experimental damper can be tuned to each individual gun.

That's why I concurred with others in that the methodical "build it and try it out" method may produce quicker results, be they negative or positive.  Maybe a pattern will emerge from all the testing.  I hope so.

Thanks,

Taso

[cosmic]

Not damping but interesting ..