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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6.5CM vs 6.5PRC???
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<blockquote data-quote="lhp63190" data-source="post: 1876595" data-attributes="member: 96319"><p>Lots of factors at play here, but the biggest one is the stability in shooting large/heavy for caliber bullets. Berger has a twist rate calculator that tells you when your bullets are stabilized. </p><p></p><p>[URL unfurl="true"]https://bergerbullets.com/twist-rate-calculator/[/URL]</p><p></p><p>So in my case, looking at the 6.5 PRC shooting the new Berger 156 EOL at 200 ft above sea level, at a temp of 50 degrees, I would have marginal bullet stability with an 8 twist. My bullet would be fully stable in the exact same conditions w/ a 7.5 twist. My assumption is that you'll start seeing more bullet offerings for 6.5 in the 150+ grain designed for PRC. </p><p></p><p>Zog -- it looks like you are in Montana, and my guess is that your elevation would mitigate these issues and you'd probably be fine with an 8 twist in a PRC shooting large bullets, but i'm in Texas barely above sea level so it does cause problems for me. </p><p></p><p>For the record, I learned this lesson the hard way. Back when Broz was doing all the great work on the 300 WM and 215 bergers, I built a 300 WM with a 10 twist and couldn't shoot the 215's out of my gun accurately bc i needed a 9 twist barrel. It was an expensive lesson so I'm much more diligent about twist rates and the bullets i want to shoot.</p></blockquote><p></p>
[QUOTE="lhp63190, post: 1876595, member: 96319"] Lots of factors at play here, but the biggest one is the stability in shooting large/heavy for caliber bullets. Berger has a twist rate calculator that tells you when your bullets are stabilized. [URL unfurl="true"]https://bergerbullets.com/twist-rate-calculator/[/URL] So in my case, looking at the 6.5 PRC shooting the new Berger 156 EOL at 200 ft above sea level, at a temp of 50 degrees, I would have marginal bullet stability with an 8 twist. My bullet would be fully stable in the exact same conditions w/ a 7.5 twist. My assumption is that you'll start seeing more bullet offerings for 6.5 in the 150+ grain designed for PRC. Zog -- it looks like you are in Montana, and my guess is that your elevation would mitigate these issues and you'd probably be fine with an 8 twist in a PRC shooting large bullets, but i'm in Texas barely above sea level so it does cause problems for me. For the record, I learned this lesson the hard way. Back when Broz was doing all the great work on the 300 WM and 215 bergers, I built a 300 WM with a 10 twist and couldn't shoot the 215's out of my gun accurately bc i needed a 9 twist barrel. It was an expensive lesson so I'm much more diligent about twist rates and the bullets i want to shoot. [/QUOTE]
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6.5CM vs 6.5PRC???
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