Magnus Effect
A sideways aerodynamic force on a spinning bullet flying through a crosswind that contributes to vertical deflection and adds to lateral drift.
The Magnus effect is the force that arises when a spinning bullet travels through air that is moving across its line of flight. The spin drags a thin layer of air around the projectile, and in a crosswind that circulation becomes asymmetric, producing a force perpendicular to both the spin axis and the relative wind. On a stable bullet this typically shows up as a small vertical deflection, contributing to aerodynamic jump.
This force is distinct from spin drift, which comes from the gyroscopic behavior of the spinning bullet rather than from the wind itself, though both push the point of impact sideways and both feed into a careful windage call. The magnitude of the Magnus effect depends on spin rate and crosswind speed, so it interacts with the bullet’s stability factor and grows in importance at long range.