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Rifles, Reloading, Optics, Equipment
Reloading
How to tighten up my group.
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<blockquote data-quote="Bart B" data-source="post: 127114" data-attributes="member: 5302"><p>[ QUOTE ]</p><p>Bart...you sound like you have more engineering background than me. I can only go by my experience and that reported by excellent reloaders. If the barrel is so rigidly fixed and harmonics don't come into play why do so many people report tightening groups with different primers.....seating depths...slight changes in speed....ie loading up or down?</p><p></p><p>What is it that you are saying is THE THING that changes?</p><p></p><p></p><p>[/ QUOTE ]I don't have a mechanical engineering background. I have worked with and shot matches with some who do and they've shared a lot of simple physics stuff with me. One of them is the resident mechanical engineer for the US Olympic shooting team who has acutally measured how a barrel whips/vibrates when a round's fired in it.</p><p></p><p>Virtually all rifle barrels have a resonant, fundamental frequency somewhere between 40 and 80 Hz (Hz = Hertz, used to be called CPS or cycles per second). When the barrel's screwed into an action, its resonant frequency will change a little bit. And it'll change a little more when that barreled action's screwed into a stock then sights attached. </p><p></p><p>When you tap a complete rifle's barrel with something and hear that high frequency ring, that's somewhere in the 2500 to 3500 Hz range. That high-pitched sound is caused by sound waves traveling back and forth through the barreled action at about 18,000 Hz; 17 times faster than through air. This high frequency is a harmonic about 40 to 60 times the stocked barreled action's resonant frequency and is about what the top 10 piano keys make.</p><p></p><p>Most of a barrel's whip when fired is in the vertical plane. And that whip is at the resonant, low frequency. The high-pitched frequency we hear when the metal's tapped causes vibrations so small in size they are meaningless. But folks hear the ringing and it's normal they would think that this high frequency is the one that's important to timing the bullet's exit at some ideal point in the barrel's whip.</p><p></p><p>With a barrel's resonant frequency making it whip vertical somewhere between 40 and 60 Hz, that means one complete cycle will happen in 1/40th to 1/60th of a second; 25 down to 16.7 thousandths of a second, or milliseconds. Most centerfire bullets take about 4 to 5 milliseconds to leave the barrel after the firing pin's released, smacked the primer and the powder burns pushing the bullet out. Which means the bullet's gone before the barrel's barely started one whip cycle. </p><p></p><p>So I think the idea that one can shoot a bullet at the correct speed such that it leaves the barrel when the muzzle's at the top or bottom of it's whip (when the least movement is happening) is a misconception. A given rifle's barrel has only one frequency it whips at and different bullet weights have different lengths of time it takes for them to leave the barrel. I don't know of anybody who has actually measured a barrel's vertical whipping along with determining where in that cycle the bullet leaves the muzzle. But there's a lot of conjecture and opinions around as to what happens and when. As far as I'm concerned, as long as each bullet leaves at the same point in the barrel's whip cycle, best accuracy will happen. And I don't care where that point is.</p><p></p><p>I don't know all the details of why one set of components shoots more accurate than another set. Nor how changing the way a given set of components are assembled will change the accuracy produced. I don't think anyone knows all the reasons why load A shoots more accurate than load B. All I know is that accuracy is the reduction of all variables to as close to zero as possible. And some combinations of components and assembly techniques seem to work better than others.</p></blockquote><p></p>
[QUOTE="Bart B, post: 127114, member: 5302"] [ QUOTE ] Bart...you sound like you have more engineering background than me. I can only go by my experience and that reported by excellent reloaders. If the barrel is so rigidly fixed and harmonics don't come into play why do so many people report tightening groups with different primers.....seating depths...slight changes in speed....ie loading up or down? What is it that you are saying is THE THING that changes? [/ QUOTE ]I don't have a mechanical engineering background. I have worked with and shot matches with some who do and they've shared a lot of simple physics stuff with me. One of them is the resident mechanical engineer for the US Olympic shooting team who has acutally measured how a barrel whips/vibrates when a round's fired in it. Virtually all rifle barrels have a resonant, fundamental frequency somewhere between 40 and 80 Hz (Hz = Hertz, used to be called CPS or cycles per second). When the barrel's screwed into an action, its resonant frequency will change a little bit. And it'll change a little more when that barreled action's screwed into a stock then sights attached. When you tap a complete rifle's barrel with something and hear that high frequency ring, that's somewhere in the 2500 to 3500 Hz range. That high-pitched sound is caused by sound waves traveling back and forth through the barreled action at about 18,000 Hz; 17 times faster than through air. This high frequency is a harmonic about 40 to 60 times the stocked barreled action's resonant frequency and is about what the top 10 piano keys make. Most of a barrel's whip when fired is in the vertical plane. And that whip is at the resonant, low frequency. The high-pitched frequency we hear when the metal's tapped causes vibrations so small in size they are meaningless. But folks hear the ringing and it's normal they would think that this high frequency is the one that's important to timing the bullet's exit at some ideal point in the barrel's whip. With a barrel's resonant frequency making it whip vertical somewhere between 40 and 60 Hz, that means one complete cycle will happen in 1/40th to 1/60th of a second; 25 down to 16.7 thousandths of a second, or milliseconds. Most centerfire bullets take about 4 to 5 milliseconds to leave the barrel after the firing pin's released, smacked the primer and the powder burns pushing the bullet out. Which means the bullet's gone before the barrel's barely started one whip cycle. So I think the idea that one can shoot a bullet at the correct speed such that it leaves the barrel when the muzzle's at the top or bottom of it's whip (when the least movement is happening) is a misconception. A given rifle's barrel has only one frequency it whips at and different bullet weights have different lengths of time it takes for them to leave the barrel. I don't know of anybody who has actually measured a barrel's vertical whipping along with determining where in that cycle the bullet leaves the muzzle. But there's a lot of conjecture and opinions around as to what happens and when. As far as I'm concerned, as long as each bullet leaves at the same point in the barrel's whip cycle, best accuracy will happen. And I don't care where that point is. I don't know all the details of why one set of components shoots more accurate than another set. Nor how changing the way a given set of components are assembled will change the accuracy produced. I don't think anyone knows all the reasons why load A shoots more accurate than load B. All I know is that accuracy is the reduction of all variables to as close to zero as possible. And some combinations of components and assembly techniques seem to work better than others. [/QUOTE]
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How to tighten up my group.
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