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Bullet Stability Calculator

The Miller twist rule estimates the gyroscopic stability factor Sg from the bullet's weight, diameter, length, and your barrel's twist — with the published corrections for velocity and air density. Length comes from the manufacturer's product page for your bullet.

Bullet weight (gr)

Diameter (in)

Bullet length (in)

Twist (in/turn)

Muzzle velocity (fps)

Temperature (°F)

Altitude (ft)

Read this before you rely on any number here. Predictions use the standard G1/G7 drag models and the data you enter — they are estimates, not measurements, and they are never load advice. Confirm with live fire at distance. For anything you load yourself, work only from current published manuals (Hodgdon, Sierra, Hornady, Lyman), start low, and work up. TruingLog publishes no load recipes and suggests no charge weights.