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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Come on bullet makers!!!
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<blockquote data-quote="Michael Eichele" data-source="post: 467696" data-attributes="member: 1007"><p>Speed can help yes but not as much as you might think. Equal RPM for euqal RPM does not make for equal stability factors. It is true yes that sometimes when a bullet/twist combo is on the line of stability/instability for one caliber it can be suitable for a faster version such as comparing a 308 to a 30-378 but we are still talking about minor stability differences even for 1000'/sec difference you may see a stability factor of 0.10 - 0.12 change. The 308 load was 1.03 and the 30-378 (1000'/sec faster) is only 1.14. This is the difference between the ragged line and definate stability but it is still a low Sg.</p><p></p><p>A bullet that is 1.72" long, .338 in diameter, 300 grains, and is jacketed lead fired in a 13x barrel at 2600 FPS offers a 1.1 stability factor. Bump it up to 3000 FPS and the factor only goes up to 1.16 even though the RPM is 166155 up from 144000. </p><p></p><p>Using a 12x barrel you find 180000 and 156000 RPM respectively yet the Sg at 2600 FPS is 1.32 even though the RPM's of the 2600' load in the 12 twist barrel is between both velocity ranges for the 13 twist barrel. </p><p></p><p>Make it a 14.5 twist and launch them at 3400' and see that the RPM's are 168830 yet the Sg is .99 which is clearly unstable even though the RPMs are comparable to the above examples.</p><p></p><p>When it comes to stability in rifles, RPM's alone are not a reliable way to determine stability.</p><p></p><p>M</p></blockquote><p></p>
[QUOTE="Michael Eichele, post: 467696, member: 1007"] Speed can help yes but not as much as you might think. Equal RPM for euqal RPM does not make for equal stability factors. It is true yes that sometimes when a bullet/twist combo is on the line of stability/instability for one caliber it can be suitable for a faster version such as comparing a 308 to a 30-378 but we are still talking about minor stability differences even for 1000'/sec difference you may see a stability factor of 0.10 - 0.12 change. The 308 load was 1.03 and the 30-378 (1000'/sec faster) is only 1.14. This is the difference between the ragged line and definate stability but it is still a low Sg. A bullet that is 1.72" long, .338 in diameter, 300 grains, and is jacketed lead fired in a 13x barrel at 2600 FPS offers a 1.1 stability factor. Bump it up to 3000 FPS and the factor only goes up to 1.16 even though the RPM is 166155 up from 144000. Using a 12x barrel you find 180000 and 156000 RPM respectively yet the Sg at 2600 FPS is 1.32 even though the RPM's of the 2600' load in the 12 twist barrel is between both velocity ranges for the 13 twist barrel. Make it a 14.5 twist and launch them at 3400' and see that the RPM's are 168830 yet the Sg is .99 which is clearly unstable even though the RPMs are comparable to the above examples. When it comes to stability in rifles, RPM's alone are not a reliable way to determine stability. M [/QUOTE]
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