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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: 864697" data-attributes="member: 28191"><p>You are confusing Sg (gyroscopic stability) with dynamic stability. If a bullet has gyroscopic instability, it will tumble within the first 50 to 100 yards. A bullet which flies well until 500 yards, but tumbles before 600 yards is demonstrating dynamic instability. See Chapter 10 of Applied Ballistics for Long Range Shooting.</p><p></p><p>Increasing the twist rate may or may not improve dynamic stability issues. It may be that (unlike most bullets) this specific bullet is losing angular velocity faster than it is losing forward (translational) velocity. Something else may be going on. </p><p></p><p>If these bullets really had a Sg between 0.95 and 1.05, I expect the increased drag would be creating problems long before the bullet reached 500 yards. I expect the Sg is close to 1.239 (you should use the true diameter of .3075") and that dynamic instability is the source of the problem.</p></blockquote><p></p>
[QUOTE="Michael Courtney, post: 864697, member: 28191"] You are confusing Sg (gyroscopic stability) with dynamic stability. If a bullet has gyroscopic instability, it will tumble within the first 50 to 100 yards. A bullet which flies well until 500 yards, but tumbles before 600 yards is demonstrating dynamic instability. See Chapter 10 of Applied Ballistics for Long Range Shooting. Increasing the twist rate may or may not improve dynamic stability issues. It may be that (unlike most bullets) this specific bullet is losing angular velocity faster than it is losing forward (translational) velocity. Something else may be going on. If these bullets really had a Sg between 0.95 and 1.05, I expect the increased drag would be creating problems long before the bullet reached 500 yards. I expect the Sg is close to 1.239 (you should use the true diameter of .3075") and that dynamic instability is the source of the problem. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Long bullets require fast twist barrels?
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