Twist Rate & Stability Calculator

When it comes to long-range precision, your barrel’s twist rate is the absolute foundation of your bullet’s flight. The spin imparted by the rifling is what keeps your projectile stable, accurate, and cutting through the wind. If your twist rate is too slow for your bullet’s length and weight, the bullet will tumble and keyhole. If it is too fast, you risk over-stabilizing the projectile, which can magnify microscopic jacket imperfections and degrade your accuracy.

To take the guesswork out of barrel selection and load development, ballisticians use a mathematical measurement called the Gyroscopic Stability Factor (SG).

Above, you will find our interactive Twist Rate and Stability Calculator. Built on the industry-standard Don Miller Twist Rule, this tool instantly crunches your bullet dimensions, muzzle velocity, and local atmospheric conditions to give you a precise SG score. Whether you are building a custom rifle or just trying to figure out if your factory barrel will stabilize a heavier, high-BC bullet, this calculator will tell you exactly what to expect before you ever pull the trigger.

Enter your bullet dimensions or select a popular preset above to find your stability score.

Data & Expertise Credit: Ammo Wisdom The foundational ballistic data, bullet dimensions, and mathematical modeling principles integrated into this calculator were sourced and verified with the help of Ammo Wisdom.