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What determines the width of an accuracy node?

brians356 said:
PS

It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency.
Are you referring to the frequency of barrels of different stiffness? Please explain.
 
gunsandgunsmithing said:
brians356 said:
PS

It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency.
Are you referring to the frequency of barrels of different stiffness?

Not necessarily.

gunsandgunsmithing said:
Please explain.

No, thanks. Feel free to expound at length, I'll read with considerable interest.
 
brians356 said:
gunsandgunsmithing said:
brians356 said:
PS

It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency.
Are you referring to the frequency of barrels of different stiffness?

Not necessarily.

gunsandgunsmithing said:
Please explain.

No, thanks. Feel free to expound at length, I'll read with considerable interest.


I'll just say that I have been of the belief that a cantilevered beam of a given stiffness will have it's own natural frequency that stays constant..generally. So, I wish you'd either explain how I'm wrong or not make such posts. There's far too much misinformation in regard to this subject, already. Now I'm listening and am eager to learn something new on this subject, as long as it's relative.
 
Give this a read its not just about tuners and is some of the best reading on the subject, with some actual data.
http://www.varmintal.com/aeste.htm

You can learn a lot by shooting groups with different charges or seating depth on a horizontal line at 100 yds. the group poi will form a sine wave and it shows you where the barrel is pointing when the bullet leaves the muzzle. Your best groups will be the highest and lowest, just before the barrel changes direction. Obviously barrels with higher amplitude of vibration will have a taller sine wave with more vertical in between than barrels with smaller amplitudes. There is a window like everything else, too stiff will make the gun hard to tune like too whipy. Its not just the barrel though, stocks will do the same thing. I am not a fan of the new ultra stiff carbon fiber stocks, or large diameter barrels in blocks for this reason.
 
Mike, how did you get to the opinion that barrels have a natural frequency that is constant? Not disagreeing, just wanting to learn. Seems to me that frequency would be greatly affected by the pressures in the barrel as well as bullet weight.
 
gunsandgunsmithing said:
brians356 said:
gunsandgunsmithing said:
brians356 said:
PS

It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency.
Are you referring to the frequency of barrels of different stiffness?

Not necessarily.

gunsandgunsmithing said:
Please explain.

No, thanks. Feel free to expound at length, I'll read with considerable interest.


I'll just say that I have been of the belief that a cantilevered beam of a given stiffness will have it's own natural frequency that stays constant..generally. So, I wish you'd either explain how I'm wrong or not make such posts. There's far too much misinformation in regard to this subject, already. Now I'm listening and am eager to learn something new on this subject, as long as it's relative.

You're rather demanding, considering this is an open and informal forum, and that I did not purposefully or directly challenge anything you may have previously asserted, but I'll humor you anyway:

What I wrote:

"It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency."

... does not in the least contradict your statement:

"a cantilevered beam of a given stiffness will have it's own natural frequency that stays constant..generally".

(And I'll note your qualifier "generally" with mild amusement, and let it go at that.)

Anticipating your objection to my new assertion, I'll preemptively point out that another way of putting what I wrote might be: "Given a barrel of a certain stiffness, it can be vibrated with varying amplitude at it's natural frequency."
 
Mike, I'll give you a opposing idea for you to argue. The barrel is deflected down ward from gravity. The pressure in the barrel as well as the natural effect of the rifle rotating around its center of gravity start the barrel moving in its upward motion. The amount of pressure and recoil effect the amount the barrel is propelled upward. The less it is propelled the less amplitude it will have.
Alex
 
zfastmalibu said:
Mike, how did you get to the opinion that barrels have a natural frequency that is constant? Not disagreeing, just wanting to learn. Seems to me that frequency would be greatly affected by the pressures in the barrel as well as bullet weight.
I'll try to find a link, but much like a tuning fork, it is my understanding that it will ring at the same frequency(not amplitude) regardless how hard it is struck.
 
gunsandgunsmithing said:
zfastmalibu said:
Mike, how did you get to the opinion that barrels have a natural frequency that is constant? Not disagreeing, just wanting to learn. Seems to me that frequency would be greatly affected by the pressures in the barrel as well as bullet weight.
I'll try to find a link, but much like a tuning fork, it is my understanding that it will ring at the same frequency(not amplitude) regardless how hard it is struck.

Just to reiterate, for my part I am not disagreeing about the frequency. But any change in amplitude should affect where the groups center vertically on the target, the vertical size of the groups, and the "width of the node".
 
Length and diameter play into stiffness. Stiffness and composition of material play into notion of a natural excitation frequency. Energy applied might be seen to affect amplitude of sine wave, not frequency. Real world: 22-250. 28" and skinny, gives a foot of vertical at 100 with an excitatory barnes solid across a few grains of powder, yet a nice node across 0.8 grain. 6.5-284--1.4" x 30 " gives no discernible node across 4 grains of powder at 100--just one ragged hole, and dispersion at long range is largely muzzle -velocity dependent, with any 'tune' lost in the condition noise, in ladder-testing. Submit these are the type of extreme examples an engineer might like whenusing a process of analyzing a variable by amplifying it. Thus, large amplitude/low frequency and all the moreso when energy of excitation is high, vs low amplitude/ high frequency. Simple. Seymour
 
brians356 said:
gunsandgunsmithing said:
brians356 said:
gunsandgunsmithing said:
brians356 said:
PS

It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency.
Are you referring to the frequency of barrels of different stiffness?

Not necessarily.

gunsandgunsmithing said:
Please explain.

No, thanks. Feel free to expound at length, I'll read with considerable interest.


I'll just say that I have been of the belief that a cantilevered beam of a given stiffness will have it's own natural frequency that stays constant..generally. So, I wish you'd either explain how I'm wrong or not make such posts. There's far too much misinformation in regard to this subject, already. Now I'm listening and am eager to learn something new on this subject, as long as it's relative.

You're rather demanding, considering this is an open and informal forum, and that I did not purposefully or directly challenge anything you may have previously asserted, but I'll humor you anyway:

What I wrote:

"It occurs to me that larger amplitude will not necessarily be accompanied by lower frequency."

... does not in the least contradict your statement:

"a cantilevered beam of a given stiffness will have it's own natural frequency that stays constant..generally".

(And I'll note your qualifier "generally" with mild amusement, and let it go at that.)

Anticipating your objection to my new assertion, I'll preemptively point out that another way of putting what I wrote might be: "Given a barrel of a certain stiffness, it can be vibrated with varying amplitude at it's natural frequency."
My apologies if I misunderstood what you were saying. Perhaps your use of the term..."[SIZE=x-small]will not necessarily be accompanied by lower frequency was used similarly to my use of "generally". [/SIZE]
[SIZE=x-small]I simply asked for clarification. Now you have given it, and I thank you. Me being "demanding", got the job done.[/SIZE] :)


I don't claim to be a vibration analysis engineer, so I was honestly hoping to learn something from someone that might have been qualified to help. I and others have a great interest in learning more about this subject and it's sometimes hard to separate the wheat from the chafe. I wasn't looking for an argument. The way I read it, your post inferred a different frequency was attainable from a barrel, unmodified. I was asking an honest question as to possibly learn from it.
 
zfastmalibu said:
Mike, I'll give you a opposing idea for you to argue. The barrel is deflected down ward from gravity. The pressure in the barrel as well as the natural effect of the rifle rotating around its center of gravity start the barrel moving in its upward motion. The amount of pressure and recoil effect the amount the barrel is propelled upward. The less it is propelled the less amplitude it will have.
Alex
I agree, Alex. This is and can still be a positive thread. Please don't let my misunderstanding of Brian's post to take it off track.
 
seymour fish said:
Length and diameter play into stiffness. Stiffness and composition of material play into notion of a natural excitation frequency. Energy applied might be seen to affect amplitude of sine wave, not frequency.

It gets even more complicated when we consider that the barrel is not attached to a massive rigid anchor, but to a gunstock of widely varying mass and shape, and which is not much constrained from moving in several directions.
 
Mike:

The frequency will change as the OD of the barrel changes, along with the diameter of the bore. The length isn't going to make a difference. For instance, if you strike a piano key for C2 (65.4 HZ) you will indeed hear 65.4 HZ. If you strike a C2 chime, you will not hear 65.4 HZ. In fact, you will not even hear 180 HZ.
 
Mike, you are correct. Brians356, you are also correct, with the caveat that the width of the node found in a wide amplitude system can be quite acceptably wide for a given purpose, whereas the width of the node for a postulated system of near-zero amplitude and ultra-high frequency could likely not be resolved, as would appear infinite excepting vertical dispersion at long range due to variation in MV. See above post for couple real-world extreme examples. Seymour
 
JRS said:
Mike:

The frequency will change as the OD of the barrel changes, along with the diameter of the bore. The length isn't going to make a difference. For instance, if you strike a piano key for C2 (65.4 HZ) you will indeed hear 65.4 HZ. If you strike a C2 chime, you will not hear 65.4 HZ. In fact, you will not even hear 180 HZ.
I will "generally" refer to barrels by their respective stiffness moreso than size OR length.


As many of you know, I build and sell tuners. I'd leke to see the conversation encompass them and how they work. It's already on that pat IMO.


Tuners do change the frequency the barrel vibrates at.


Even as a maker of tuners, I still find GOOD info hard to find and I certainly don't know everything that's going on, but I do read and research the subject extensively. With my tuner, I simply took a theory and have done my best to improve upon it and tuner design as a whole. People much more qualified than myself have given it a huge thumbs up. A few of those people are extremely qualified, but learning all that they have to offer isn't a 5 minute crash course matter.


There will be independent test results finished pretty soon, as well as testing done by some big names in the industry. My claim is that I feel like it is a step in the right direction in tuner design, not the end all, be all. Preliminary test results do show significant improvement and the test results will put quantitative numbers as to why...--Mike
 
seymour fish said:
Mike, you are correct. Brians356, you are also correct, with the caveat that the width of the node found in a wide amplitude system can be quite acceptably wide for a given purpose, whereas the width of the node for a postulated system of near-zero amplitude and ultra-high frequency could likely not be resolved, as would appear infinite excepting vertical dispersion at long range due to variation in MV. See above post for couple real-world extreme examples. Seymour

I'm not a physical scientist or mechanical engineer, but I am a software engineer and hold a degree in mathematics. What you say makes perfect sense to me. Thanks!
 
seymour fish said:
JRS, You have lost me, as when I strike a pipe, then cut it in half and strike it again, it rings at higher frequency. Seymour
Absolutely! Barrel stiffness is a more fitting description than other nomenclature, IMO. Stiffness increases greatly with shortening.
 

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