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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
220 Swift, twist rate, barrel length
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<blockquote data-quote="Mikecr" data-source="post: 1153849" data-attributes="member: 1521"><p>I wanted to add a point about choice in stability.</p><p>There are stability calculators out there that provide stability(Sg) numbers for you like 1.0 (just stable) -1.3 (marginally stable) -1.5 (fully stable).</p><p>In load developments I've seen twice where marginal stability shot worse. In both cases shifting to a shorter/higher stability bullet(of the same weights) greatly improved grouping.</p><p></p><p>My range is at sea level +/-2' depending on tide. My measure of air density conditions is calibrated per metrology lab at work, and my software is really good.</p><p>I've watched stability as a dominant change, have a bigger affect than I thought it would.</p><p></p><p>Bryan Litz(Berger) recommends at least Sg 1.5, and I'm compelled to agree all the way.</p><p>I really don't believe that over-spinning bullets (within reason) will have a worse affect than marginal stability or worse. </p><p>Sg climbs as the bullet slows downrange (before transonic) to the point that a 105VLD leaving the muzzle at 3Kfps and Sg 1.5 will climb to Sg 4.5 by 1kyds. This doesn't hurt a thing. Right?</p><p>But if you don't have enough spin to cover muzzle release well(biggest disturbance), downrange stability is too late anyway. The damage is already done.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 1153849, member: 1521"] I wanted to add a point about choice in stability. There are stability calculators out there that provide stability(Sg) numbers for you like 1.0 (just stable) -1.3 (marginally stable) -1.5 (fully stable). In load developments I've seen twice where marginal stability shot worse. In both cases shifting to a shorter/higher stability bullet(of the same weights) greatly improved grouping. My range is at sea level +/-2' depending on tide. My measure of air density conditions is calibrated per metrology lab at work, and my software is really good. I've watched stability as a dominant change, have a bigger affect than I thought it would. Bryan Litz(Berger) recommends at least Sg 1.5, and I'm compelled to agree all the way. I really don't believe that over-spinning bullets (within reason) will have a worse affect than marginal stability or worse. Sg climbs as the bullet slows downrange (before transonic) to the point that a 105VLD leaving the muzzle at 3Kfps and Sg 1.5 will climb to Sg 4.5 by 1kyds. This doesn't hurt a thing. Right? But if you don't have enough spin to cover muzzle release well(biggest disturbance), downrange stability is too late anyway. The damage is already done. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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220 Swift, twist rate, barrel length
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