When a sniper shoots a long-range target, if he is in the northern hemisphere, the bullet is deflected to the right. Conversely, if he is in the southern hemisphere, the bullet is deflected to the left.
The phenomenon occurs because the Earth is spherical and rotating.
The amount of deflection is relatively small compared to the target distance. At the range of 900 m (1000 yd), the muzzle velocity of 820 m/s and at 45° North, the amount of deflection is about 8 cm (3 in).
This phenomenon occurs because of the Coriolis effect which in turn caused by the fact that the Earth is a rotating sphere. The farther the shooter from the equator, the higher the amount of deflection.
Another related effect is the Eötvös effect. The bullet is not going to stay straight forever. It will drop and hit the target lower than what was aimed at. The amount of drop is higher for bullets fired to the West than ones shot to the East.
Such a phenomenon is also the result of the fact that the Earth is a rotating sphere. A bullet fired to the West has a smaller centrifugal force and would have higher effective weight than bullets fired to the East.
References
- The illustration is Mark Wahlberg from the poster of the movie Shooter (2007). In the movie, the Coriolis effect was mentioned briefly.
- External Ballistics – Wikipedia
- Point Mass Trajectory Calculator – JBM Ballistics
- Long Range Shooting: External Ballistics – The Coriolis Effect – The Loadout Room
- Coriolis Effect – YouTube