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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
BALLISTIC COEFFICIENTS/Twist Rates
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<blockquote data-quote="Kevin Thomas" data-source="post: 418277" data-attributes="member: 15748"><p>I don't know if this will answer any of the questions raised here, but I ran a series of BC firings that are reprinted in the Sierra Manual (3rd or 4th Edition, I think?) which addresses this exact issue. I shot a series of bullets through rifles of differing twists, in both .224" and .308" bore sizes. In the .224" as I recall I think I went with 1x7", 1x8", 1x9", 1x10", 1x12" and 1x14" using the 69 grain SMK. In the 30s, I went with 190s in a 1x8", 1x9" 1x10" 1x11" 1x12" and 1x14". Bill McDonald plotted out the results, and they were interesting. Bottom line here was, as Bryan had indicated, very little change in BC so long as the bullets were stable. As the SF approached 1.0, the scatter of the individual shots (the ES and SD of the BCs observed) opened up dramatically. As they dipped below an SF of 1.0, we continued to see round bullet holes (perhaps some excessive yaw, but no actual tumbling at that point) this scatter became general, with extremely reuced BC figures, as you'd expect. The point to this was to take both bullets from twists where they were "overstabilized" (no such thing, but it expresses the idea well) to a point where they were truly unstable, plotting the BC changes along the way. By way of full disclosure, the firings were done at 200-300 meters, which is all had available to me in the tunnel.</p><p> </p><p>Kevin Thomas</p><p>Lapua USA</p></blockquote><p></p>
[QUOTE="Kevin Thomas, post: 418277, member: 15748"] I don't know if this will answer any of the questions raised here, but I ran a series of BC firings that are reprinted in the Sierra Manual (3rd or 4th Edition, I think?) which addresses this exact issue. I shot a series of bullets through rifles of differing twists, in both .224" and .308" bore sizes. In the .224" as I recall I think I went with 1x7", 1x8", 1x9", 1x10", 1x12" and 1x14" using the 69 grain SMK. In the 30s, I went with 190s in a 1x8", 1x9" 1x10" 1x11" 1x12" and 1x14". Bill McDonald plotted out the results, and they were interesting. Bottom line here was, as Bryan had indicated, very little change in BC so long as the bullets were stable. As the SF approached 1.0, the scatter of the individual shots (the ES and SD of the BCs observed) opened up dramatically. As they dipped below an SF of 1.0, we continued to see round bullet holes (perhaps some excessive yaw, but no actual tumbling at that point) this scatter became general, with extremely reuced BC figures, as you'd expect. The point to this was to take both bullets from twists where they were "overstabilized" (no such thing, but it expresses the idea well) to a point where they were truly unstable, plotting the BC changes along the way. By way of full disclosure, the firings were done at 200-300 meters, which is all had available to me in the tunnel. Kevin Thomas Lapua USA [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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BALLISTIC COEFFICIENTS/Twist Rates
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