The simple **two arms model** adequatly describes the yawing motion
of spin-stabilized bullets, resulting from the action of all aerodynamic
moments.

The yawing motion can be understood as a superposition of a **fast**
and a **slow** **oscillation**, often called **nutation** and
**precession**.

Imagine to look at the bullet from the rear. The **slow mode arm**
CG to A should be hinged at the CG and rotates with the **slow mode frequency**.
Consequently A moves on a circle around the CG (the **red** circle).
The **fast mode arm** A to T, where T is the bulletīs tip, should be
hinged at A and rotates with the** fast mode frequency**. Thus, T rotates
on a circle about A. CG to T is the projection of the bulletīs longitudinal
axis.

An animation of the two arms model is shown in the figure below.

One additionally has to consider that the fast mode frequency **exceeds**
the slow mode frequency (which is true in the animation) and the arm lengths
CG to A and A to T are continuously shortened (which is **not** true
in the animation) if the bullet is **dynamically** stable.