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The Magnus moment
The Magnus force, which applies at its centre of pressure CPM can be
substituted by a force of the same magnitude and direction, which applies
at the CG, plus a moment, which is said to be the Magnus moment
MM
This moment tries to rotate the bullet about an axis, perpendicular to
the longitudinal axis of the bullet.
However, the gyroscopic effect also applies for the Magnus moment and
the bullet´s axis will be shifted into the direction of the moment. Thus,
as far as the conditions of the figure above are valid, the Magnus moment
will have a stabilizing effect as it tends to decrease the
angle of yaw d.
It can be easily shown that this is only true, if the centre of pressure
of the Magnus force CPM is located behind the CG. The Magnus force
destabilizes the bullet and increases the angle of yaw, if
its centre of pressure is located ahead of the CG, which may come
true in a specific velocity regime.
  
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