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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Improved Stability Formula for Plastic Tipped Bullets
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<blockquote data-quote="Michael Courtney" data-source="post: 591818" data-attributes="member: 28191"><p>The effect of the plastic tip is usually to change the gyroscopic stability (Sg) by 15-30%. It does not have a big effect on the center of gravity or the moments of inertia, but it does move the center of pressure forward. </p><p></p><p>The consequence of just using the total length in the original Miller twist rule is that the rule predicts that some plastic-tipped bullets will be unstable when they are, in fact, stable. This will restrict the user to shorter bullets with Sg's much higher than they need to be and leave the shooter with the mistaken impression that some longer, usually higher BC, bullets will not be stable in a particular rifle with given environmental conditions. </p><p></p><p>The article in PS not only presents the formula, but also discusses a lot of the science behind it. Don Miller's previous articles on stability are also highly recommended background. Here are some links:</p><p></p><p><a href="http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_1.pdf" target="_blank">http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_1.pdf</a></p><p></p><p><a href="http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_2.pdf" target="_blank">http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_2.pdf</a></p></blockquote><p></p>
[QUOTE="Michael Courtney, post: 591818, member: 28191"] The effect of the plastic tip is usually to change the gyroscopic stability (Sg) by 15-30%. It does not have a big effect on the center of gravity or the moments of inertia, but it does move the center of pressure forward. The consequence of just using the total length in the original Miller twist rule is that the rule predicts that some plastic-tipped bullets will be unstable when they are, in fact, stable. This will restrict the user to shorter bullets with Sg's much higher than they need to be and leave the shooter with the mistaken impression that some longer, usually higher BC, bullets will not be stable in a particular rifle with given environmental conditions. The article in PS not only presents the formula, but also discusses a lot of the science behind it. Don Miller's previous articles on stability are also highly recommended background. Here are some links: [URL]http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_1.pdf[/URL] [URL]http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_2.pdf[/URL] [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Improved Stability Formula for Plastic Tipped Bullets
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