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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Twist rate, how fast is too fast?
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<blockquote data-quote="Greyfox" data-source="post: 2458792" data-attributes="member: 10291"><p>This is an interesting thread. I'm in the process of doing some testing with twist rate with my 6.5x284's. I have traditionally run 140-143gr bullets(G7 BC .3-.32) in the 3000FPS range. Using 8TW barrels my SG's fall in the 1.5-1.8 range depending on the bullet and the altitude/temperature. Under these conditions, I have been able to consistently generate precision/ES in the .25MOA/ES<15FPS. 1000 yard accuracy is maintained within .5MOA and I get good terminal performace on game from 200-1000 yards. I have used this formula for over a dozen years and it has proven to be nuts-on for my LRH. When I load the 156 Berger EOL in my 8TW(which is Berger's minimum recommendation), I'm at marginal stability(SG147) at 300 ft Alt, and just over stable at 2700FT at SG 1.57, 1.7 at 4500FT). My precision/ES with the 156's, while not as good as good as the 140-143 bullets, is quite acceptable loosing about .25MOA accross the board with the 156's. But this may have nothing to do with twist rate. I(reluctantly) just mounted the same brand/chamber/dimension barrel in a 1.75TW on my rifle. This twist rate adds about .2-.3 SG across the board placing me in the full stability range with the 156's at 1.6-1.8SG, and 1.8-2.0SG with the 140-143's. </p><p>I will be most curious to observe the effects of this change. With the hopes of picking up stability with the 156's, I would also WANT to maintain my current performance with the 140 class bullets. Berger broadly says yes. I'm inclined to think that a .5 twist rate change shouldn't be a big deal. I have made much greater changes then this with my .223's with little effect using the lighter bullets. Perhaps my skepticism is a needless concern due to my OCD when it comes to fine precision, Combine this with an earlier competitive life where bullets(308) performed best at a particular spin rate window, where I observed this to actually be the case with the bullet designs of those days. </p><p>Any relevant experiences or insights would be appreciated.</p></blockquote><p></p>
[QUOTE="Greyfox, post: 2458792, member: 10291"] This is an interesting thread. I’m in the process of doing some testing with twist rate with my 6.5x284’s. I have traditionally run 140-143gr bullets(G7 BC .3-.32) in the 3000FPS range. Using 8TW barrels my SG’s fall in the 1.5-1.8 range depending on the bullet and the altitude/temperature. Under these conditions, I have been able to consistently generate precision/ES in the .25MOA/ES<15FPS. 1000 yard accuracy is maintained within .5MOA and I get good terminal performace on game from 200-1000 yards. I have used this formula for over a dozen years and it has proven to be nuts-on for my LRH. When I load the 156 Berger EOL in my 8TW(which is Berger’s minimum recommendation), I’m at marginal stability(SG147) at 300 ft Alt, and just over stable at 2700FT at SG 1.57, 1.7 at 4500FT). My precision/ES with the 156’s, while not as good as good as the 140-143 bullets, is quite acceptable loosing about .25MOA accross the board with the 156’s. But this may have nothing to do with twist rate. I(reluctantly) just mounted the same brand/chamber/dimension barrel in a 1.75TW on my rifle. This twist rate adds about .2-.3 SG across the board placing me in the full stability range with the 156’s at 1.6-1.8SG, and 1.8-2.0SG with the 140-143’s. I will be most curious to observe the effects of this change. With the hopes of picking up stability with the 156’s, I would also WANT to maintain my current performance with the 140 class bullets. Berger broadly says yes. I’m inclined to think that a .5 twist rate change shouldn’t be a big deal. I have made much greater changes then this with my .223’s with little effect using the lighter bullets. Perhaps my skepticism is a needless concern due to my OCD when it comes to fine precision, Combine this with an earlier competitive life where bullets(308) performed best at a particular spin rate window, where I observed this to actually be the case with the bullet designs of those days. Any relevant experiences or insights would be appreciated. [/QUOTE]
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Twist rate, how fast is too fast?
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