1. If you pm me with your email address, then I'll send you an excel workbook that calculates Greenhill, Dell, Powley and Miller twist rates simultaneously. 2. This workbook says that with your inputs, .321", 1.05", 185 gr, 1500 fps, 16" twist, Greenhill twist is 14.7" Dell twist is 13.3" Powley s.f. is 2.01 Miller s.f. is 1.44 vs. 1.46 3. Powley and Miller use s.f. in the calculations. With s.f. of 1.5,Powley twist is 18.5"; Miller twist is 15.6" 4. Your question assumes that the 16" twist is correct, and there is clear disagreement amongst these four regarding "correct" twist. At the Powley/iller stage there are a set of 6 major variables, dia, length, wt., mv, s.f. and twist. We must know 5 to know the 6th. 5. I suspect that the difference may lie in the definition of "twist". Greenhill twist is the minimum twist required for bullet stability, and except for very long range with large calibers, it works. There is no recorded instance of Greenhill failing under 600 yards.
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