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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Long bullets require fast twist barrels?
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<blockquote data-quote="Michael Courtney" data-source="post: 865150" data-attributes="member: 28191"><p>Of course, the claim of the Miller and Courtney-Miller twist formulas is an expected uncertainty of 5%. This means the standard deviation of the bell curve is 5% of the mean. In contrast, the standard deviation of the bell curve for the Greenhill formula is more like 50%. The claim is for usefulness, not for absolute truth. The measure of usefulness for empirical formulas is their uncertainty, not their absolute truth in the sense of exactness with no errors. </p><p></p><p>To date, the published Miller and Courtney-Miller twist formulas have proved to be accurate within 5% for all applicable cases for which experimental data is available. Don's original papers (2005 and 2009) include data validating the accuracy of his twist formula in 14 different bullets. Since 2011, we've collected data carefully validating the accuracy of the twist formulas in 11 different bullets. </p><p></p><p>In Don's 2009 paper, he pointed out the inapplicability of the original twist formula for plastic tipped bullets. We fixed that problem with an improved formula published in 2012. We are currently tweaking the formula to reduce the uncertainty in cases where it applied to open tipped bullets with a significant air space in the front. </p><p></p><p>The point about firing bullets base first is somewhat academic with almost no practical application. However, we have actually fired a number of bullets base first and can report in all cases we've tried, bullets fired base first are actually more stable in flight than those fired nose first. There are some practical challenges in loading and shooting bullets base first, but if one overcomes these difficulties, we expect that a successfully launched bullet will remain in stable flight (base first) if the formulas predict stable flight nose first.</p></blockquote><p></p>
[QUOTE="Michael Courtney, post: 865150, member: 28191"] Of course, the claim of the Miller and Courtney-Miller twist formulas is an expected uncertainty of 5%. This means the standard deviation of the bell curve is 5% of the mean. In contrast, the standard deviation of the bell curve for the Greenhill formula is more like 50%. The claim is for usefulness, not for absolute truth. The measure of usefulness for empirical formulas is their uncertainty, not their absolute truth in the sense of exactness with no errors. To date, the published Miller and Courtney-Miller twist formulas have proved to be accurate within 5% for all applicable cases for which experimental data is available. Don's original papers (2005 and 2009) include data validating the accuracy of his twist formula in 14 different bullets. Since 2011, we've collected data carefully validating the accuracy of the twist formulas in 11 different bullets. In Don's 2009 paper, he pointed out the inapplicability of the original twist formula for plastic tipped bullets. We fixed that problem with an improved formula published in 2012. We are currently tweaking the formula to reduce the uncertainty in cases where it applied to open tipped bullets with a significant air space in the front. The point about firing bullets base first is somewhat academic with almost no practical application. However, we have actually fired a number of bullets base first and can report in all cases we've tried, bullets fired base first are actually more stable in flight than those fired nose first. There are some practical challenges in loading and shooting bullets base first, but if one overcomes these difficulties, we expect that a successfully launched bullet will remain in stable flight (base first) if the formulas predict stable flight nose first. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Long bullets require fast twist barrels?
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