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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Complete formula
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<blockquote data-quote="Michael Eichele" data-source="post: 478682" data-attributes="member: 1007"><p>If you want to do it easily and quickly by hand without 'lengthy derivations', I suggest you get a hand held computer and use ballistic software. If you really must know, there are good formulas in the Sierra reloading manual 4th addition.</p><p></p><p>Yes the are formulas that relate to twist rate and bullet stability (see the Miller system below).</p><p></p><p><strong>([Bullet Weight]*30)/(([Twist Rate]/[Cal])^2*[Cal]^3*[Bullet Length]/[Cal]*(1+([Bullet Length]/[Cal])^2))*([Velocity]/2800)^(.333)*(([Temprature]+460)/(519)*29.92/[Barometric_Pressure])</strong></p><p><strong></strong></p><p><strong>What you are looking to do with this formula is to apply different twists to come up with a stability factor. 1.0 is concidered barely stable, 1.1 is adequete where 1.35-1.5 is optimum. At least at 1.35 you have some forgivness if you drop major elevation and are in colder temps. A 1.35 could become a 1.2 factor where a 1.1 could become unstable in cold dense enviornments.</strong></p><p><strong></strong></p><p><strong>Bullet weight in grains, caliber in inches, bullet length in inches, velocity in FPS, Temp in F and barometric pressure in inches of hg.</strong></p><p></p><p>The greenhill method is easier but not nearly as optimum.</p></blockquote><p></p>
[QUOTE="Michael Eichele, post: 478682, member: 1007"] If you want to do it easily and quickly by hand without 'lengthy derivations', I suggest you get a hand held computer and use ballistic software. If you really must know, there are good formulas in the Sierra reloading manual 4th addition. Yes the are formulas that relate to twist rate and bullet stability (see the Miller system below). [B]([Bullet Weight]*30)/(([Twist Rate]/[Cal])^2*[Cal]^3*[Bullet Length]/[Cal]*(1+([Bullet Length]/[Cal])^2))*([Velocity]/2800)^(.333)*(([Temprature]+460)/(519)*29.92/[Barometric_Pressure]) What you are looking to do with this formula is to apply different twists to come up with a stability factor. 1.0 is concidered barely stable, 1.1 is adequete where 1.35-1.5 is optimum. At least at 1.35 you have some forgivness if you drop major elevation and are in colder temps. A 1.35 could become a 1.2 factor where a 1.1 could become unstable in cold dense enviornments. Bullet weight in grains, caliber in inches, bullet length in inches, velocity in FPS, Temp in F and barometric pressure in inches of hg.[/B] The greenhill method is easier but not nearly as optimum. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Complete formula
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