Gyroscopic Stability & Drift Calculator

[IanP]

A lot of people are curious about barrel twist rates and bullet stability and for good reason. Nobody wants to waste their money on a barrel that wont stabilise the bullet they have chosen for use in competition (or hunting).

Everyone now knows about Bryan Litz's book "Applied Ballistics For Long Range Shooting" and how by using the software included with the book you can obtain the Sg (stability factor) for your bullet. Bryan recommends a Sg of around 1.4 for optimal stability but a bullet with an Sg of 1.0 or more is regarded as stable.

The other interesting aspect of gyroscopic stability is gyroscopic drift (spin drift). A 308W may drift around 8 inches to the right at 1000 yards just thru this effect. If the rifle twist is to the right then bullets will drift to the right and vice versa.

If you have not got Bryan's book yet, then I have made available for download an Excel spreadsheet that does both of these things. The only inputs you need are your rifle and bullet data along with the bullet time of flight which you get from a ballistics program.

The spreadsheet calculator file is here: http://www.safclass.com.au/downloads.html

A free ballistics program from Berger Bullets can be downloaded here: http://www.bergerbullets.com/Ballistics ... index.html

Its now pretty easy to check your bullet stability and gyro drift thanks largely to Bryan Litz making this information so easy to understand and use!

Ian