Projectile Stability and Twist Rate Calculator
Projectile Characteristics
Mass (m) — grains
Diameter (d) — in
Length — in
Environmental & Velocity Factors
Temperature — °F
Altitude — ft
Pressure — in Hg
Velocity — fps
Apply Subsonic / Long-Aspect Correction
?
Automatic (Mach < 1 & ℓ > 4.0)
The standard Miller formula assumes supersonic velocities and overestimates stability for subsonic projectiles.
This correction activates automatically for subsonic, long-aspect projectiles but can be manually toggled for edge cases.
Twist rate (T) — in/turn
1:11
slower spin — 1:24
1:7 — faster spin
unstable
< 1.0
marginal
1.0–1.5
stable
1.5–2.5
over
> 2.5
Sg =
—
—
Enter projectile parameters and set the twist rate above.