What determines the width of an accuracy node?

[gunsandgunsmithing]

If reducing vibration is your only concern, shoot a lighter bullet at higher velocities. Otherwise, there is but one option. Install a tuner, and relocate the vibration.

Changing bullets or velocity wouldn't change the barrel's natural frequency, only the amplitude. And that's dependent on if it takes the same energy to move a lighter bullet faster as to push a heavier bullet slower. I think. This all makes a dumb old county boy's head hurt.
We all have to realize that frequency and amplitude are independent of one another. They are separate and not related.

 

[JRS]

Not the frequency Mike, but the vibration time would be shortened, even though it's a pretty short time already. A thirty caliber bullet traveling at 3000+ FPS is in the barrel for only 0.0011 of a second.

Though a 45ACP and 22WMR operate at the same pressure, the 22 leaves the barrel much sooner than it's big brother

 

[gunsandgunsmithing]

Not the frequency Mike, but the vibration time would be shortened, even though it's a pretty short time already. A thirty caliber bullet traveling at 3000+ FPS is in the barrel for only 0.0011 of a second.

Though a 45ACP and 22WMR operate at the same pressure, the 22 leaves the barrel much sooner than it's big brother

Ok, while I still believe for purposes of this discussion, that it takes the same energy to push a slow, heavy bullet as a fast light bullet, resulting in equal amplitude of vibration...and that neither would change the natural frequency of the barrel, I think I see your point. In bore time certainly would change tune if tuned is timing bullet exit with muzzle position...So I think we agree.


Tuners are much easier to use than to understand, but I want to know all that I can in this regard, even though it may not matter one bit to how we can shoot with a tuner, properly adjusted for best potential.

 

[seymour fish]

Jrs, Couple thoughts: what role do you see bearing surface length playing regards vibratory amplitude height, and have you considered another option--vibration damping--instead of movement of the vibratory node? Mike's tuner incorporates both. I have played with use of a tuner and a separate magneto-viscoelastic-mechanical damper in rimfire with positive results on target, by placing said damper at the null. Other attempts at damping: Anschutz cork-like bedding material, original boss patent calling for rubber-like bedding material. Seymour

 

[JRS]

Exactly Mike

Though it has nothing to do with a barrel…. when I change the strings on my guitar to a heavier gauge string, the sustain [vibration] lasts much longer.

 

[JRS]

Jrs, Couple thoughts: what role do you see bearing surface length playing regards vibratory amplitude height, and have you considered another option--vibration damping--instead of movement of the vibratory node? Mike's tuner incorporates both. I have played with use of a tuner and a separate magneto-viscoelastic-mechanical damper in rimfire with positive results on target, by placing said damper at the null. Other attempts at damping: Anschutz cork-like bedding material, original boss patent calling for rubber-like bedding material. Seymour

Actually, the dampening material didn't work out too well for me. We ran into the same problem with the ENORMOUS amount of vibrations created by the steam generators in the nuke plants. Millions of dollars later, the only solution was the use of snubbers [shock absorbers if you will].

 

[gunsandgunsmithing]

Jrs, Couple thoughts: what role do you see bearing surface length playing regards vibratory amplitude height, and have you considered another option--vibration damping--instead of movement of the vibratory node? Mike's tuner incorporates both. I have played with use of a tuner and a separate magneto-viscoelastic-mechanical damper in rimfire with positive results on target, by placing said damper at the null. Other attempts at damping: Anschutz cork-like bedding material, original boss patent calling for rubber-like bedding material. Seymour

Seymour, are you saying that the original BOSS call for rubber(or similar) bedding? I've not heard that. That's very interesting. You may remember me advocating for a bedding similar to this in rimfire, on another forum.

 

[Alex Wheeler]

Mike, the point I am trying to make is that a barrel with pressure and a bullet in it does not have a natural frequency. When the bullet is in the bore it is part of the barrels mass. As it moves down the bore the barrels mass is moving. Same idea as a tuner, you are just moving the barrels mass. You can also change the mass of the barrel by changing the weight of the bullet. So IMO, the frequency and amplitude of a barrel can be altered with the load.

 

[Alex Wheeler]

There is also alot of talk about vibration dampening. Vibration is what allows you to tune a barrel. If you damp it too much you now have a gun that is not tuneable. What you want is a system with the right vibration that allows you to tune for your goals. Ever shoot a tiny group at 100 with a 100 fps spread? Vibrations are what makes that happen. Same as shooting a 3" group at 1k with a 15-20 fps spread.

 

[seymour fish]

Mike, Yes, I read that a number of years back. It is fascinating that perhaps the amount of amplitude we desire is domain-specific. In rimfire, even with the ';best' ammo, the ES tends to be very large as a percentage of MV, thus tight groups require the use of positive compensation. Perhaps the same is true to some degree for F-t/r where max barrel length to obtain velocity and meet weight limits overrides desire for barrel stiffness out of necessity, even though we can tightly control ES with loading. Suspect the reverse may be 'true' for shortrange centerfire benchrest, but defer to your thoughts there, where your accomplishments speak loudly.

Seymour p.s. Mike, I missed your thoughts on rimfire damping. can you refer me to the source please sir?

 

[seymour fish]

Zfast, I gave some extreme examples of just this in an above post on this thread, and agree that as long as there is ES, some tunability might give best accuracy, but only at the distance you tune for. I find 3 clicks on the tuner are required to optimize from 50 yards to 100 yards for exactly this reason, in rimfire. Now consider a scenario where you could achieve zero ES and zero muzzle movement over the entire firing sequence from firing pin fall to well beyond bullet exit. Would this give precision on target? Seymour

 

[JRS]

Not meant as an argument, but, the tuner doesn't move the barrel's mass Alex. It counteracts/relocates the vibration. The bullet is in the barrel for such a short period of time that it contributes nothing whatsoever to mass, but does with vibration.

 

[Alex Wheeler]

Seymour, I am a big believer in positive compensation for long range shooting. I build my guns using it as a guideline. Zero es and zero muzzle movement will not give zero groups because the rest of the barrel will still be moving. There are many vibration modes.

JRS, the tuner works by moving mass. That is what a tuner is, a movable mass. And a minute amount of movement has a large effect, so in no way do I believe the weight of the bullet has no effect on the barrels vibration. And in no way to I believe its not in the barrel long enough. All we care about is what happens when the bullet is in the barrel.

I am enjoying this thread.

 

[JRS]

Alex:

As I stated, the weight of the bullet DOES in fact contribute to the vibration. The lighter the bullet, the less time it has to induce vibration. As for the tuner, it most certainly can't move the barrels mass. It relocates the vibration from one point, to another.

 

[seymour fish]

Zfast, I posed the question to bring radial expansion of the barrel, and the timing of it, into the discussion. Enjoying this thread too. Seymour

 

[Alex Wheeler]

JRS, if you agree the bullets has an effect on vibration, how does it do it? With mass. While the bullet is in the barrel it becomes part of the barrel's mass. Like a tuner. When the tuner is on the barrel it becomes part of the barrel's mass, when you turn the tuner you are moving the barrels mass. Call it the tuner/barrel combined mass if you want. I don't really care about the terminology. The barrel is not independent of the tuner or the bullet, so they have to be looked at as a unit. When you speak of the tuner, you only speak of its effect. What is it doing to achieve that effect? Moving mass.

 

[Alex Wheeler]

Zfast, I posed the question to bring radial expansion of the barrel, and the timing of it, into the discussion. Enjoying this thread too. Seymour

I have not done much studying on that particular mode. I think there was some speculation to its existence. Anything you would like to add on the subject would be great.

 

[gunsandgunsmithing]

JRS, if you agree the bullets has an effect on vibration, how does it do it? With mass. While the bullet is in the barrel it becomes part of the barrel's mass. Like a tuner. When the tuner is on the barrel it becomes part of the barrel's mass, when you turn the tuner you are moving the barrels mass. Call it the tuner/barrel combined mass if you want. I don't really care about the terminology. The barrel is not independent of the tuner or the bullet, so they have to be looked at as a unit. When you speak of the tuner, you only speak of its effect. What is it doing to achieve that effect? Moving mass.

Tuners move the center of mass and in turn, where the nodes form.

 

[Alex Wheeler]

JRS, if you agree the bullets has an effect on vibration, how does it do it? With mass. While the bullet is in the barrel it becomes part of the barrel's mass. Like a tuner. When the tuner is on the barrel it becomes part of the barrel's mass, when you turn the tuner you are moving the barrels mass. Call it the tuner/barrel combined mass if you want. I don't really care about the terminology. The barrel is not independent of the tuner or the bullet, so they have to be looked at as a unit. When you speak of the tuner, you only speak of its effect. What is it doing to achieve that effect? Moving mass.

Tuners move the center of mass and in turn, where the nodes form.

No argument from me.

 

[Alex Wheeler]

Mike I would like to hear your opinion as to if you feel the moving bullet in the bore would have an effect on the frequency of the barrel?