April 5, 2023Berger Twist Rate Stability Calculator
The Berger Bullets website has a handy Twist Rate Stability Calculator. It predicts your gyroscopic stabilization factor (SG) using multiple variables: bullet length, bullet weight and velocity. This cool tool will tell you if your bullet will stabilize in your barrel.
How to use Berger’s Twist rate Calculator
It is easy to use the Twist Rate Calculator. Simply enter the bullet DIAMETER (e.g. .264), bullet WEIGHT in grains and bullet overall LENGTH in inches. Berger provides these details on its website for all types of bullets. For other brands, we recommend that you weigh three bullets and measure the length of three of them. The average weight and length of all three should be used. Simply enter your bullet data along with observed Muzzle Velocity and outside Temperature and click “Calculate SSG” to calculate bullet stability. You can try different twist rates (and recalculate), until you reach a SG value of 1.4 or higher.
Berger’s Twist Rate Calculator gives a predicted stability value, called “SG” (for “Gyroscopic Sability”). This is the Gyroscopic Stability applied by the bullet by spinning. This number is calculated from the basic equation: (rigidity and spinning mass/overturning aerodynamic torque) Your bullet will not stabilize if it has a SG below 1.0. Your bullet may not stabilize if it has a SG between 1.0 and 1. Your bullet should stabilize if your SG is greater than 1.1. However, stabilization may not be sufficient when temperature, altitude or other variables are less than optimal. Berger recommends at least 1.5 SG to break out of the “Marginal Safety” zone. Bryan Litz (Berger Ballistician), recommends at least a 1.4 SG rating for selecting a barrel twist to fit a particular bullet. This allows you to shoot in a variety of conditions such as higher or lower temperatures or altitudes. We welcome submissions from readers.
