Your browser version is outdated. We recommend that you update your browser to the latest version.

>>>> ON TARGET LIKE A FALCON >>>>)



News Flash

Jan 2022: Release of app update.

Feb 2021: Added Utilities to calculate Stability Factor, Spin Drift, Coriolis and Eotvos effects, and speed of sound. 

Miller Stability and Spin Drift

The Miller Stability factor is an indication of how stable a bullet will remain in flight.  A minimum value of 1.5 ensures that a bullet will remain stable across most temperatures and atmospheric variations.  The stability factor is used to calculate spin drift.  If you also wish to calculate spin drift, enter the time of flight with the rest of the input variables.  See Miller, Don, “How Good are Simple Rules for Estimating Rifling Twist”, Precision Shooting, June 2009, Pg 48-52 for the equation to calculate stability.

Spin Drift (inches) = 1.25*(Miller Stability Factor + 1.2)*tof^1.83


NOTE: All values must be entered by the user. Otherwise a NaN answer will result.


Bullet Weight (grains)
Bullet Diameter (inches)
Bullet Length (inches)
Muzzle Velocity (fps)
Twist Rate (inches/turn)
Time of Flight (seconds)



Miller Stability Factor
Spin Drift (inches)