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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6mm creedmoore build. what twist should i choose for light varmint bullets
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<blockquote data-quote="Hugnot" data-source="post: 3041153" data-attributes="member: 115658"><p>I have three, 6mm rifles - .243W (8 twist), 6mm CM (8 twist), & 6mm AI (10 twist). The 8 twist rifles are only used with 105 grain bullets. The 6mm AI is only used with 87 VMax bullets at 3475 average FPS. My guess is the 6mm CM would get 3300 fps with the 87 Vmax.</p><p></p><p>Running the Miller Sg estimator for the 87 Vmax, 88 Berger FB, & 80 Nosler BT with 9 & 10 twist barrels:</p><p></p><p>[ATTACH=full]546287[/ATTACH]</p><p></p><p>As evident, substantial RPM's are churned up with 9 & 10 twist barrels. My thoughts are that bullets don't have perfect rotational balance densities (moment of rotational inertia) and the higher rpms exasperate minor balance deviations. An 8 twist would generate more RPM's. Going with this, I generally shoot 105's from the 8 twist barrels & 87 from the 10 twist 6mm AI at 3475 fps.</p><p></p><p>Either a 9 or 10 twist would work just fine with these bullets. I have had 2 barrels on my 6mm AI and I like the 87's with the 10 twist. I have used the 87 Vmax @ 3475 against rodents with great & exciting results - bang, zip, SPLAT at 1/4 mile & more. My last shot with the 6mm AI was last week, I hit 3 inch steel at 300 & blew the target off stand -I will offer gun club compensation to fix so I can keep hitting it. Kinetic energy is substantial with higher velocities, square of velocity.</p><p></p><p>The 87 VMax despite it's modest BC value of .4 ( G1) is a terrific longish range performer at just under 3500 FPS, like 600 yards. A 6mm CM would come real close. The 6mm CM having a 10 twist would be close to optimum with these light bullets & provide small rifle primer brass. My 8 T 6mm CM gives great results with 105's but when loaded with 87 VMax never has equaled the accuracy of the 10 T 6mm AI with 87's.</p><p></p><p>Consider the 87 Vmax bullets.</p></blockquote><p></p>
[QUOTE="Hugnot, post: 3041153, member: 115658"] I have three, 6mm rifles - .243W (8 twist), 6mm CM (8 twist), & 6mm AI (10 twist). The 8 twist rifles are only used with 105 grain bullets. The 6mm AI is only used with 87 VMax bullets at 3475 average FPS. My guess is the 6mm CM would get 3300 fps with the 87 Vmax. Running the Miller Sg estimator for the 87 Vmax, 88 Berger FB, & 80 Nosler BT with 9 & 10 twist barrels: [ATTACH type="full" alt="Screenshot (848).png"]546287[/ATTACH] As evident, substantial RPM's are churned up with 9 & 10 twist barrels. My thoughts are that bullets don't have perfect rotational balance densities (moment of rotational inertia) and the higher rpms exasperate minor balance deviations. An 8 twist would generate more RPM's. Going with this, I generally shoot 105's from the 8 twist barrels & 87 from the 10 twist 6mm AI at 3475 fps. Either a 9 or 10 twist would work just fine with these bullets. I have had 2 barrels on my 6mm AI and I like the 87's with the 10 twist. I have used the 87 Vmax @ 3475 against rodents with great & exciting results - bang, zip, SPLAT at 1/4 mile & more. My last shot with the 6mm AI was last week, I hit 3 inch steel at 300 & blew the target off stand -I will offer gun club compensation to fix so I can keep hitting it. Kinetic energy is substantial with higher velocities, square of velocity. The 87 VMax despite it's modest BC value of .4 ( G1) is a terrific longish range performer at just under 3500 FPS, like 600 yards. A 6mm CM would come real close. The 6mm CM having a 10 twist would be close to optimum with these light bullets & provide small rifle primer brass. My 8 T 6mm CM gives great results with 105's but when loaded with 87 VMax never has equaled the accuracy of the 10 T 6mm AI with 87's. Consider the 87 Vmax bullets. [/QUOTE]
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6mm creedmoore build. what twist should i choose for light varmint bullets
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