Coriolis Effect

Coriolis Effect - an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force ) acting perpendicular to the direction of motion and to the axis of rotation. On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern hemisphere. The Coriolis Effect is subjective to the northern and southern hemisphere, and is independent of direction. It is, however, dependent on latitude, with the maximum effect at the poles and minimum effect at the equator. The coriolis effect is often talked about in long range shooting and referenced at a certain minimum distance. (e.g. you only need to correct for the coriolis effect at 1000 or more yards.) However, the coriolis effect is related to time of flight (tof) and not distance. Below is the formula for calculating coriolis. The easiest way to calculate and adjust for this is with ballistic tables or a ballistic calculator. F = 2 * m * v * ω * sin(α) F - is the Coriolis force, m - is the mass of the moving object, v - is the velocity of the moving object, ω - is the angular velocity of the Earth, α- is the latitude at which the object is located. Or  (Ω * Range ft2 * sin(Lat)) / V ave In layman's terms, while the bullet is in the air, the earth is moving under it. The longer the bullet is in the air (tof) the more effect there is/distance the earth traveled under the bullet. A slower bullet, 1000 fps @ 500 yards vs a faster bullet, 3000 fps @ 1500 yards (with everything being equal), will have the same time of flight and will result in the same amount of coriolis effect to adjust for, despite the difference in distance. Let's look at exactly how much of an effect coriolis has on trajectory. For this example, I'll use a 175 SMK in a .308 at 1000 yards traveling 2636 FPS. This gives a TOF of 1.72 seconds. For me, located in southern part of United States, Coriolis changes my bullet's impact by 2.4 inches. That's not a lot, but if I'm shooting a 1 MOA target (10 inches at 1000 yards) that's 1/4 the size of my target. To me, that is a lot. It's also large enough to make an adjustment on our scope. A 1/4 MOA at 1000 is 2.5 inches. So, if we can make an adjustment, we should. We should adjust for coriolis, but let's look at it from a different angle. Let's compare the adjustment for coriolis to the difference between a wind call of 10 and 11 MPH at 1000 yards. A 10 mph wind at 1000 yards pushes the bullet 102.7 inches and an 11 mph wind push the bullet 113 inches. Thats 10 inches of difference between reading the wind wrong by 1 mph. So, your coriolis adjustment can easily get lost on a wind call. I still think it's important to adjust for coriolis so you don't learn to read wind incorrectly. The Overwatch