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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Optimum 7mm-08 twist rate
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<blockquote data-quote="VinceMule" data-source="post: 2696253" data-attributes="member: 122164"><p>I found that the proper twist rate for the bullets you want to shoot provides a larger tune window on powder charges. Also for game, over twisting the RPM's can cause more rapid bullet expansion, a good or bad thing? Additional RPM's do cause cup and core bullets to shed their jackets faster, this Is well known. As barrels get well worn with alligator hide throats, fire cracked badly, bullet jackets are stressed. Stressed bullet jackets MAY perform differently in expansion and accuracy, especially if the bullet is jumping to the lands.</p><p></p><p>There is another consideration, and that is what is acceptable accuracy for you. While one guy is happy with one-inch groups at 100, the next guy wants 1/4 MOA for longer-range shooting.</p><p></p><p>Spending some time on a ballistics calculator can teach you a lot about the twist rate you need for your hunting/shooting conditions.</p><p></p><p>Pressure can drop as you DECREASE your twist rate to the max limit vs a very fast twist. For example, I built a custom 7 STW, 27", Pac Nor super match, zero freebore reamer, for shooting the 140g Nosler Accubonds. 3650 fps was the accuracy node where the barrel shot in the 2's, opening up a single bullet hole using Win brass, fed 215's, and IMR 7828 with an 11 Twist, three groove barrel. 120g Barnes TTSX was doing 3900 fps, opening up a bullet hole with its groups.</p><p></p><p>In a custom 7 Mag, the only time I run into trouble with Berger 180g vld-h is in extremely cold weather with a 9T.</p><p></p><p>I have also ran the 180g Hornady ELD-M in the 9T, again with warm weather.</p><p></p><p>Again, I would urge all to invest some time on a twist rate calculator, twist for your circumstances, ONLY! Don't go 8 Twist just because it sounds cool.</p><p></p><p>For all 162-168g bullets, a 9Twist is more than adequate....run the numbers.</p></blockquote><p></p>
[QUOTE="VinceMule, post: 2696253, member: 122164"] I found that the proper twist rate for the bullets you want to shoot provides a larger tune window on powder charges. Also for game, over twisting the RPM's can cause more rapid bullet expansion, a good or bad thing? Additional RPM's do cause cup and core bullets to shed their jackets faster, this Is well known. As barrels get well worn with alligator hide throats, fire cracked badly, bullet jackets are stressed. Stressed bullet jackets MAY perform differently in expansion and accuracy, especially if the bullet is jumping to the lands. There is another consideration, and that is what is acceptable accuracy for you. While one guy is happy with one-inch groups at 100, the next guy wants 1/4 MOA for longer-range shooting. Spending some time on a ballistics calculator can teach you a lot about the twist rate you need for your hunting/shooting conditions. Pressure can drop as you DECREASE your twist rate to the max limit vs a very fast twist. For example, I built a custom 7 STW, 27", Pac Nor super match, zero freebore reamer, for shooting the 140g Nosler Accubonds. 3650 fps was the accuracy node where the barrel shot in the 2's, opening up a single bullet hole using Win brass, fed 215's, and IMR 7828 with an 11 Twist, three groove barrel. 120g Barnes TTSX was doing 3900 fps, opening up a bullet hole with its groups. In a custom 7 Mag, the only time I run into trouble with Berger 180g vld-h is in extremely cold weather with a 9T. I have also ran the 180g Hornady ELD-M in the 9T, again with warm weather. Again, I would urge all to invest some time on a twist rate calculator, twist for your circumstances, ONLY! Don't go 8 Twist just because it sounds cool. For all 162-168g bullets, a 9Twist is more than adequate....run the numbers. [/QUOTE]
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Optimum 7mm-08 twist rate
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