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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Berger Twist Rate Stability Calculator (need help)
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<blockquote data-quote="Mikecr" data-source="post: 2024337" data-attributes="member: 1521"><p>Less stability.</p><p>The 9 in 9tw or 1:9 means 9" travel per bullet turn.</p><p>That is 9" of resistance to point forward travel that a bullet revolution is trying to compensate for. That resistance is air density, so resultant stability from a fixed turn rate is very heavily tied to air density.</p><p>Given this, twist rate requirements are always reported as based on sea level standard air density conditions. That's your beginning consideration.</p><p></p><p>So for example: If your hunting is at 1200ft above sea level, and warmer than sea level standard 59deg, then your air density is less,, less resistance to point forward bullet travel,, you can get away with further distance between bullet turns. A slower twist rate.</p><p></p><p>Bill, based on your data either 7 or 8tw are plenty. I would go 8 or even 9 myself.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 2024337, member: 1521"] Less stability. The 9 in 9tw or 1:9 means 9" travel per bullet turn. That is 9" of resistance to point forward travel that a bullet revolution is trying to compensate for. That resistance is air density, so resultant stability from a fixed turn rate is very heavily tied to air density. Given this, twist rate requirements are always reported as based on sea level standard air density conditions. That's your beginning consideration. So for example: If your hunting is at 1200ft above sea level, and warmer than sea level standard 59deg, then your air density is less,, less resistance to point forward bullet travel,, you can get away with further distance between bullet turns. A slower twist rate. Bill, based on your data either 7 or 8tw are plenty. I would go 8 or even 9 myself. [/QUOTE]
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Berger Twist Rate Stability Calculator (need help)
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