August 16th 2021
Berger Twist Rate Stability Calculator 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 “CalculateSG” to calculate bullet stability. You can try different twist rates (and recalculate), until you reach a SG value of 1.4 or higher.
Gyroscopic Stability and Twist Rate
Berger’s Twist Rate Calculator gives a predicted stability value, called “SG” (for “Gyroscopic Sability”). This is the Gyroscopic Stability applied on the bullet by spinning. This number is calculated from the basic equation: (rigidity and spinning mass)/(overturning aerodynamic force).
Your bullet will not stabilize if your SG is below 1.0. Your bullet may not stabilize if your SG is 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 in order to get out of “Marginal Stability”.
His book Applied Ballistics For Long-Range Shooting (3rd Edition) Bryan Litz (Berger Ballistician), recommends a minimum 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 higher or lower temperatures or altitudes.
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Tags: Berger Calculator, Bryan Litz, Bullet RPM, Bullet Stability, Gyroscopic Stability, Twist Rate Calculator
