It can be found from a mathematical treatment that the bullet's longitudinal axis and the direction of the velocity of the CG deviate by a small angle, which is said to be the equilibrium yaw or the yaw of repose . For right-handed spin bullets, the bullet's axis of symmetry generally points to the right and a little bit upward with respect to the direction of the velocity vector- indicating the direction into which the CG moves - , just as shown in the figure .
As an effect of this small inclination, there is a continuous air stream, which tends to deflect the bullet to the right. Thus the occurrence of the yaw of repose is the reason for bullet drift to the right (for right-handed spin) or to the left (for left-handed spin).
Usually, the yaw of repose is a very small angle and measures only fractions of a degree. The figure shows the variation of the yaw of repose angle along the trajectory for a 7.62 x 51 NATO M80 bullet fired at 32°. Although, in this example, the yaw of repose never exceeds half a degree, the resulting side drift at impact almost amounts to 100 yards.