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Rifles, Reloading, Optics, Equipment
Reloading
5 or 3 shot group when determining ES/SD???
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<blockquote data-quote="Bart B" data-source="post: 626443" data-attributes="member: 5302"><p>I also stated that some shots at higher velocity struck low; I had put each group into thirds of all shots fired.</p><p></p><p>Even if every bullet left at exactly the same speed at exactly the same point in the vertical whip of the barrel, they'll still have vertical dispersion. That's due to the bullets small spread in BC; they all ain't the same 'cause they ain't all perfectly balanced. The more unbalanced ones will have more drag and therefore strike lower. There' typically no more than 1.5% spreads in BC, but that's enough to cause 1/4 MOA vertical spread at 1000 yards.</p><p></p><p>I think you mean the barrel, when at it's node, it's straight and at the mid point in its whip cycle. I don't think anybody can guarantee that'll ever happen as the bullet exits and nobody's ever proved it as far as I know. Spark photograph tests decades ago showed an M1903 Springfield's bore axis at the muzzle was moving upward and close to the top of its whip when the bullet exited. With most rifle barrels bore axis at the muzzle whipping at their fundamental frequencies of 60 to 100 Hz, they go through one cycle in about 17 to 10 milliseconds (other harmonic frequencies are higher and have much, much smaller magnitudes). Barrel time from case mouth to out the muzzle for most rifle bullets is only about 1 to 1.5 milliseconds. And the angular speed of the muzzle axis' whip at this node or zero point is the fastest; it's the slowest at the peak and valley of the wave.</p><p></p><p>Here's a link that'll help explain how a barrel whips. Check out all the site's links to barrel movements when they're whipping about.</p><p></p><p><a href="http://www.varmintal.com/amode.htm" target="_blank">Barrel Harmonics Mode Shape Movies</a></p><p></p><p>No, I'm not an engineer any more. But that doesn't matter.</p></blockquote><p></p>
[QUOTE="Bart B, post: 626443, member: 5302"] I also stated that some shots at higher velocity struck low; I had put each group into thirds of all shots fired. Even if every bullet left at exactly the same speed at exactly the same point in the vertical whip of the barrel, they'll still have vertical dispersion. That's due to the bullets small spread in BC; they all ain't the same 'cause they ain't all perfectly balanced. The more unbalanced ones will have more drag and therefore strike lower. There' typically no more than 1.5% spreads in BC, but that's enough to cause 1/4 MOA vertical spread at 1000 yards. I think you mean the barrel, when at it's node, it's straight and at the mid point in its whip cycle. I don't think anybody can guarantee that'll ever happen as the bullet exits and nobody's ever proved it as far as I know. Spark photograph tests decades ago showed an M1903 Springfield's bore axis at the muzzle was moving upward and close to the top of its whip when the bullet exited. With most rifle barrels bore axis at the muzzle whipping at their fundamental frequencies of 60 to 100 Hz, they go through one cycle in about 17 to 10 milliseconds (other harmonic frequencies are higher and have much, much smaller magnitudes). Barrel time from case mouth to out the muzzle for most rifle bullets is only about 1 to 1.5 milliseconds. And the angular speed of the muzzle axis' whip at this node or zero point is the fastest; it's the slowest at the peak and valley of the wave. Here's a link that'll help explain how a barrel whips. Check out all the site's links to barrel movements when they're whipping about. [url=http://www.varmintal.com/amode.htm]Barrel Harmonics Mode Shape Movies[/url] No, I'm not an engineer any more. But that doesn't matter. [/QUOTE]
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5 or 3 shot group when determining ES/SD???
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