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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Need some rifle twist experts to help me out...
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<blockquote data-quote="Gerard Schultz" data-source="post: 901235" data-attributes="member: 51"><p>You are welcome.</p><p></p><p>For general information it must also be considered that all stability calculators are not intended for all bullets. Any calculator based on the Miller formula for instance, cannot be used to calculate anything other than lead or jacketed lead core bullets. For a different specific gravity (SG) such as copper or brass, one would need a calculator based on the method developed by McCoy. </p><p></p><p>A typical Miller formula calculator would ask for caliber, weight, length, twist, speed, temperature and altitude. The McCoy method, in addition to the parameters of the Miller formula, also asks for ogive length, meplat diameter, material density, boat tail length, boat tail angle and the shape of the ogive. </p><p></p><p>Take a solid copper bullet and enter the following data in a Miller based formula for gyroscopic stability (Sg). </p><p></p><p>Caliber: .300 (Humor me)</p><p>Weight: 150gr</p><p>Length: 1.25"</p><p>Twist: 10"</p><p>Speed: 3000fps</p><p>Temperature: 59</p><p>Altitude: 0</p><p></p><p>The Sg calculated would be about 2.1</p><p></p><p>Enter the above data into a McCoy calculator as well as:</p><p></p><p>Ogive Length: 0.669"</p><p>Meplat Diameter: 0.087"</p><p>Material Density (SG): 8.95</p><p>Boat Tail Length: 0.244"</p><p>Base Diameter: 0.256"</p><p>Head Shape: 1 (for a typical slender bullet forebody)</p><p></p><p>The calculated Sg would be around 1.66 which is correct for solid copper.</p><p></p><p>Finding a McCoy calculator: Search for "McCoy Twist Rate Formula"</p></blockquote><p></p>
[QUOTE="Gerard Schultz, post: 901235, member: 51"] You are welcome. For general information it must also be considered that all stability calculators are not intended for all bullets. Any calculator based on the Miller formula for instance, cannot be used to calculate anything other than lead or jacketed lead core bullets. For a different specific gravity (SG) such as copper or brass, one would need a calculator based on the method developed by McCoy. A typical Miller formula calculator would ask for caliber, weight, length, twist, speed, temperature and altitude. The McCoy method, in addition to the parameters of the Miller formula, also asks for ogive length, meplat diameter, material density, boat tail length, boat tail angle and the shape of the ogive. Take a solid copper bullet and enter the following data in a Miller based formula for gyroscopic stability (Sg). Caliber: .300 (Humor me) Weight: 150gr Length: 1.25" Twist: 10" Speed: 3000fps Temperature: 59 Altitude: 0 The Sg calculated would be about 2.1 Enter the above data into a McCoy calculator as well as: Ogive Length: 0.669" Meplat Diameter: 0.087" Material Density (SG): 8.95 Boat Tail Length: 0.244" Base Diameter: 0.256" Head Shape: 1 (for a typical slender bullet forebody) The calculated Sg would be around 1.66 which is correct for solid copper. Finding a McCoy calculator: Search for "McCoy Twist Rate Formula" [/QUOTE]
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