Does anyone have information about the Greenhill method for calculating gyro stability. For example what twist do I need to stabilize a 30 cal, 180 gr at 3100 fps.

The greenhill formula really is overly conservative for this purpose.

If you are willing to do the measurements, you can get much closer to the right answer at the JBM link below. HTH, Dutch.

http://www.eskimo.com/~jbm/