Twist Rate & Stability Calculator

Compute gyroscopic stability (Sg) using the Miller Twist Rule^*. Sg values above 1.5 are considered stable.

Manufacturer

Bullet

Selecting a bullet prefills diameter, length, and weight (you can override).

Barrel Twist (in/turn)

Example: 10 = 1:10”

Muzzle Velocity (fps)

Diameter (in)

Length (in)

Weight (gr)

Temperature (°F)

ISA sea-level default: 59 °F

Pressure (inHg)

Preset to ISA sea-level pressure. Entering Altitude overrides this value. (Default: 29.92 inHg)

Altitude (ft)

* The classic Miller model assumes a jacketed boat-tail bullet with fairly uniform density. Flat-base bullets are excluded when positively identified, but some may still appear in the selection list. For these bullets, predicted stability can be slightly conservative (lower than actual).