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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Twist vs Bullet Weight Question
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<blockquote data-quote="Mikecr" data-source="post: 2938116" data-attributes="member: 1521"><p>Twist requirement is expressed with displacement per turn. This holds, regardless of velocity.</p><p>It IS NOT expressed in turns per time (RPMs). That absolutely fails all tests.</p><p>Higher velocities change where a bullet is in it's drag curve at any given moment. Drag changes the center of pressure, and Sg totally follows a bullet's drag curve.</p><p>It is VERY rare that velocity alone will bail anyone out of a stability issue, because drag does still go up (overall) with the square of velocity.</p><p></p><p>Changing Sg does nothing to change the overturning moment arm. That remains.</p><p>What changes is the gyroscopic inertia to overcome the moments.</p><p></p><p>This is true. Both a mass change, and center of mass change, can occur with either addition or deletion of weight.</p><p>So a simple change in bullet weight, in itself, is meaningless to stability.</p><p>You couldn't declare that a heavier bullet will always be more or less stable with a given twist rate. That will fail tests as Calvin45 has pictured.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 2938116, member: 1521"] Twist requirement is expressed with displacement per turn. This holds, regardless of velocity. It IS NOT expressed in turns per time (RPMs). That absolutely fails all tests. Higher velocities change where a bullet is in it's drag curve at any given moment. Drag changes the center of pressure, and Sg totally follows a bullet's drag curve. It is VERY rare that velocity alone will bail anyone out of a stability issue, because drag does still go up (overall) with the square of velocity. Changing Sg does nothing to change the overturning moment arm. That remains. What changes is the gyroscopic inertia to overcome the moments. This is true. Both a mass change, and center of mass change, can occur with either addition or deletion of weight. So a simple change in bullet weight, in itself, is meaningless to stability. You couldn't declare that a heavier bullet will always be more or less stable with a given twist rate. That will fail tests as Calvin45 has pictured. [/QUOTE]
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Twist vs Bullet Weight Question
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