Stability calculators work well if the right calculator is applied to do the math. Most calculators determine the static stability and very few will calculate dynamic stability and tractability. Static stability is what most of us are interested in and it is important to use a method that gives us close to the right numbers.

Static stability is also called gyroscopic stability and is abbreviated as Sg (SG is the abbreviation for specific gravity) and Sd is the abbreviation of dynamic stability (SD is the abbreviation for sectional density).

An easy way of checking the window of application of a calculator is to see what it asks for.

The Greenhill formula is simplistic in that it asks only for the bullet length and caliber. It cannot calculate the shape of the bullet because it does not ask for the dimensions. It works only for the calculation of lead or jacketed lead bullets in use more than a century ago. It is no longer applicable.

The Miller formula also asks for weight, twist, speed, temperature and altitude. It is an expanded formula over the Greenhill one and works with jacketed lead core bullets. It was not designed to deal with monometal bullets, secant or tangent ogives, larger/smaller meplats, flatbase/boat tail/vld bullets or hollow points. All these factors influence the center of gravity of the bullet and the Sg of the bullet in a given twist rate of the barrel.

To more accurately calculate the stability factor of a bullet with a boat tail, anything other than a standard ogive, large meplat (as in FN), small meplat (as in long range hunting) or monometallic, the McCoy formula works better. The McCoy method asks for all that the Greenhill and Miller methods ask for as well as the ogive length and shape, base diameter, meplat diameter, boat tail length, density (SG) and existing twist rate.

For example, when you click on the bullet number to get to a particular bullet profile, all the twist and stability data on that page are calculated with the McCoy method.

The McCoy method used to be available as a downloadable file for older versions of Windows but that seems to have stopped. I am looking around for a way to overcome this but it is not easy to find an IT person this time of the year.