determing twist rate and optimum velocity 7mm bore

[Ballisticboy]

ok that makes sense and it explains why those 175gr ELD's I had wouldn't stabilize in my rifle at a starting low velocity, which means low rpms if I understand correctly and even with the outdated millers equation it called for a twist of 1-8.5 for that same ELD bullet that I had so much trouble with

The actual RPM does not determin gyroscopic stability, it is the ratio between RPM and velocity which is one of the factors. The true equation for gyroscopic stability factor (SG) at the muzzle does not even contain velocity or spin rate. What the equation does contain is the aerodynamic overturning moment coefficient which varies with speed, peaking at just below Mach 1 for low drag bullet shapes (drag makes no contribution to gyroscopic or aerodynamic stability) which is why gyroscopic stability is a minimum at speeds just below Mach 1.

 

[crustyrusty]

so there is no simple way to explain a truism between velocity and rpm's(by extension twist rate of the barrel) = stability? it would seem that if you could go too fast( a blown up bullet) you can go to slow ( a keyhole hit) I did watch a you tube vid that touched on aerodynamic overturning coefficient and where it places the center of gravity in the bullet just forward of the center of the length of said bullet to lead nose first and as velocity bleeds off it moves backwards...I hope I got the Idea right