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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability: Fine Points to be Aware Of
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<blockquote data-quote="Mikecr" data-source="post: 2633609" data-attributes="member: 1521"><p>There are a couple errors in this (perspective-wise).</p><p></p><p>1. A bullet that groups at all at 100yds will not hit a tumbling concern again until transonic. This, because gyroscopic stability increases as a bullet travels down range, all the way to transonic. The biggest free flight destabilizing moment is muzzle release. This is why bullets that will tumble generally do so immediately (within 10yds). They don't just decide to tumble on their own later.</p><p></p><p>2. Gyroscopic stability has nothing to do with RPMs. Stability requirements are not expressed in turns per time, but displacement per turn. Displacement being air density, and turns being imparted by rifling twist.</p><p>So an 8:1 twist requirement is 8" of a standard air density, per 1 turn, to gyroscopically overcome the overturning drag in that 8".</p><p>Doesn't matter the velocity, or resultant turns per time. You need one turn per every 8", and this is set by twist.</p><p></p><p>I understand that you're going at this from a terminal ballistic standpoint, but you cannot muddle these things in external ballistics to do it.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 2633609, member: 1521"] There are a couple errors in this (perspective-wise). 1. A bullet that groups at all at 100yds will not hit a tumbling concern again until transonic. This, because gyroscopic stability increases as a bullet travels down range, all the way to transonic. The biggest free flight destabilizing moment is muzzle release. This is why bullets that will tumble generally do so immediately (within 10yds). They don't just decide to tumble on their own later. 2. Gyroscopic stability has nothing to do with RPMs. Stability requirements are not expressed in turns per time, but displacement per turn. Displacement being air density, and turns being imparted by rifling twist. So an 8:1 twist requirement is 8" of a standard air density, per 1 turn, to gyroscopically overcome the overturning drag in that 8". Doesn't matter the velocity, or resultant turns per time. You need one turn per every 8", and this is set by twist. I understand that you're going at this from a terminal ballistic standpoint, but you cannot muddle these things in external ballistics to do it. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Stability: Fine Points to be Aware Of
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