A Spinning Planet: Explaining the Coriolis Effect

January 31, 2023
Photo by Dustin Ellermann, Whittington Center Range. The Coriolis Effect is used for extreme long-range shots such as this (2100 meters at Raton in New Mexico). The Earth’s rotation actually moves the target a short distance (in space) over the course of the bullet’s flight. This is why it looks very stable when you’re at the range. It is actually a huge sphere that zooms through space while spinning around its own axis, one turn per 24 hours. Extreme long-range shooters may have problems with the earth’s rotation. The planet’s rotation can cause a deflection in the bullet path over long distances. This is the ballistics manifestation the Coriolis Effect. Bryan Litz, of Applied Ballistics, discusses the Coriolis Effect in his Ballistics Books & Seminars. Bryan points out that Coriolis is a “very subtle effect.” Because it seems mysterious, people like to make more of it. Coriolis is irrelevant in most shooting situations within 1K. The Effect is less than one click at 1000 yards for most cartridge types. The Coriolis Effect can be lost in the noise even if you are shooting at 1000 yards in windy conditions. Bryan says that even in calm conditions, the Coriolis Effect can be “lost in the noise” at extreme ranges. The principle behind shooting from one point on a rotating globe to another is that you are using an inertial reference frame. This means that if the bullet’s flight time is very long, it can cause the bullet to drift away from its target. The amount of apparent drift is negligible, and it all depends on the planet’s latitude and azimuth. Coriolis is a subtle effect. You must travel at least 1000 yards with typical bullet BCs and velocities before Coriolis is even one click. Bryan says that the Coriolis Effect should not be considered when moving targets are being shot at. It should also not be considered in uncertain wind conditions. There are variables that can influence your uncertainty picture and the Coriolis can distract you more than it is worth. Coriolis can have a significant impact on your hit percentage if you shoot at long ranges with small targets in low wind conditions. Coriolis will creep in to areas where you have a good understanding of your muzzle velocity (BC) and other conditions. If you include Coriolis on these types of shots, your ballistics solutions will be more refined and accurate. Coriolis is not important in most long-range shooting situations. It is important to understand when you should think about it, and when you shouldn’t. It is important to understand when it will be useful and when it won’t. “Similar Posts” Tags:Ballistics, Bryan Litz and Dustin Ellermann. Earth Rotation, ELR. Extreme Long Range. Whittington Center.