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Engineering
Mechanical Engineering
Calculating Miller Stability
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[QUOTE="Dr. Courtney, post: 6025338, member: 117790"] Hi. I helped Don Miller with the testing of his original twist rate formula and also helped him modify the formula to apply to plastic tipped bullets and later to open tipped match bullets. We co-authored two articles on bullet stability that appeared in Precision Shooting in 2012, shortly before Don passed away. Send me a PM and we'll work out how to get you a copy of the stability calculator spreadsheet, which applies the same formulas as the JBM site for computing stability. I would note that using an actual barometric pressure (as measured with something like a Kestrel weather meter) is far preferable to computing pressures from altitudes. Once you have the stability, the formula for spin drift is from Bryan Litz and explained in more detail here: [URL]http://forum.accurateshooter.com/threads/spin-drift-calculation.3862266/[/URL] The Litz formula for spin drift (which JBM also uses) is empirical - an engineer determined it works well through experimental testing. It is not based on rigorous theoretical results (neither are the stability formulas). It is known that stability tends to increase as a bullet flies downrange, but the Litz formula uses the stability at the muzzle. The constants in his spin drift formula account for that, but they may give varying results for bullets whose spin slows at different rates. But changing it puts you in the realm of developing new formulas and computational methods that have not been tested rather than using established and tested results. Experiments that reliably test tweaks in computing spin drift are difficult, because you need to exclude other confounding factors (wind, Coriolis, etc.) [/QUOTE]
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Calculating Miller Stability
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