Dillon Arms

Gyroscopic (static) stability factor

Static stability factor (example)

This figure shows the gyroscopic stability factor of the 7.62 x 51 Nato bullet M80, fired at an angle of departure of 32°, a muzzle velocity of 870 m/s and a rifling pitch at the muzzle of 12 inches. The M80 bullet shows static stability over the whole flight path as the static stability condition sg>1 is fulfilled everywhere. The value of sg adopts a minimum of 1.35 at the muzzle.

Generally it can be stated that if a bullet is statically stable at the muzzle, it will be statically stable for the rest of its flight. This can be easily understood from the fact, that the static stability factor is proportional to the ratio of the bulletīs rotational and transversal velocity (see formula Go to formula). As the the rotational velocity is much less damped than the transversal velocity (which is damped due to the action of the drag), the static stability factor increases, at least for the major part of the trajectory.

Bullet and gun designers usually prefer sg > 1.2 ..1.5 at the muzzle, however it has been observed that many handgun bullet show excessive static stability.

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