December 25th, 2015

Shooting Science: The Coriolis Effect Explained

Whittington Coriolis Effect
The Coriolis Effect comes into play with extreme long-range shots like this. The rotation of the earth actually moves the target a small distance (in space) during the course of the bullet’s flight. Photo by Dustin Ellermann at Whittington Center Range.

Coriolis Effect Bryan Litz Applied BallisticsWhen you’re out at the range, the Earth seems very stable. But it is actually a big sphere zooming through space while spinning around its axis, one complete turn every 24 hours. The rotation of the earth can create problems for extreme long-range shooters. During extended bullet flight times, the rotation of the planet causes an apparent deflection of the bullet path over very long distances. This is the ballistics manifestation of the Coriolis Effect.

Bryan Litz of Applied Ballistics has produced a short video that explains the Coriolis Effect. Bryan notes that Coriolis is “a very subtle effect. People like to make more of it than it is because it seems mysterious.” In most common shooting situations inside 1K, Coriolis is not important. At 1000 yards, the Effect represents less than one click (for most cartridge types). Even well past 1000 yards, in windy conditions, the Coriolis Effect may well be “lost in the noise”. But in very calm conditions, when shooting at extreme ranges, Bryan says you can benefit from adjusting your ballistics solution for Coriolis.

Bryan explains: “The Coriolis Effect… has to do with the spin of the earth. You are basically shooting from one point to another on a rotating sphere, in an inertial reference frame. The consequence of that is that, if the flight time of the bullet gets significantly long, the bullet can have an apparent drift from its intended target. The amount [of apparent drift] is very small — it depends on your latitude and azimuth of fire on the planet.”

Coriolis Effect Bryan Litz Applied Ballistics

Coriolis is a very subtle effect. With typical bullet BCs and velocities, you must get to at least 1000 yards before Coriolis amounts to even one click. Accordingly, Bryan advises: “Coriolis Effect is NOT something to think about on moving targets, it is NOT something to think about in high, uncertain wind environments because there are variables that are dominating your uncertainty picture, and the Coriolis will distract you more than the correction is worth.”

“Where you could think about Coriolis, and have it be a major impact on your hit percentage, is if you are shooting at extended range, at relatively small targets, in low-wind conditions. Where you know your muzzle velocity and BC very well, [and there are] pristine conditions, that’s where you’re going to see Coriolis creep in. You’ll receive more refinement and accuracy in your ballistics solutions if you account for Coriolis on those types of shots. But in most practical long-range shooting situations, Coriolis is NOT important. What IS important is to understand is when you should think about it and when you shouldn’t, i.e. when applying it will matter and when it won’t.”

The Coriolis Effect — General Physics
The Coriolis Effect is the apparent deflection of moving objects when the motion is described relative to a rotating reference frame. The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object’s speed in the rotating frame.

A commonly encountered rotating reference frame is the Earth. The Coriolis effect is caused by the rotation of the Earth and the inertia of the mass experiencing the effect. Because the Earth completes only one rotation per day, the Coriolis force is quite small, and its effects generally become noticeable only for motions occurring over large distances and long periods of time. This force causes moving objects on the surface of the Earth to be deflected to the right (with respect to the direction of travel) in the Northern Hemisphere and to the left in the Southern Hemisphere. The horizontal deflection effect is greater near the poles and smallest at the equator, since the rate of change in the diameter of the circles of latitude when travelling north or south, increases the closer the object is to the poles. (Source: Wikipedia)

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December 25th, 2015

Happy Holidays to Our Readers — Thanks for Your Support

Christmas tree snow

Christmas Elk CanadaHoliday Greetings to Our Readers
Merry Christmas and Happy Holidays to all our readers and especially our nearly 30,000 Forum Members. This marks our our 11th Christmas “in business”, and the site is stronger than ever thanks to our members and industry sponsors. (and are now accessed by over 550,000 visitors every month. Part of the reason for that success is the hard work of our volunteer helpers.

Unsung Heroes Deserve Recognition
I want to acknowledge some guys who have really helped out the site. Number one is JayChris, our IT guy — he keeps the servers running smoothly and maintains our Forum. Jay has been working through the holidays on a major Forum upgrade we hope to roll out at year’s end. This is a big undertaking, requiring great technical expertise. Jay deserves our thanks for all his hard work and his dedication… working nights and weekends to keep this big project on schedule. Thanks also go to Jeff Williams, our “Answerman” who fields miscellaneous questions from our readers. We have a great place to test rifles thanks to our good buddy (and designated trigger-puller) Joe Friedrich. Special thanks go to the 6.5 Guys, Ed Mobley and Steve Lawrence, who authored our latest Cartridge Guide, and contributed SHOT Show videos. I also want to recognize our regular contributors, including Vince Bottomley, German S., Jason Baney, Robert Whitley, Tony Chow, Mark LaFevers, and Gavin Gear. And we must acknowledge Boyd Allen and EdLongRange who tirelessly supply story leads for the Daily Bulletin. These guys (and many others) have all contributed much time and effort.

We also want to thank our major sponsors, without whose support the site could not provide the full experience, with an active Forum, an archive of in-depth articles, and fresh content 365 days a year in our Daily Bulletin. We’re grateful to all our sponsors and advertisers. In particular, I want to acknowledge Shiraz Balolia, a great friend of the shooting sports, and a gifted marksman in his own right. Shiraz has provided key support for this site though his companies and Grizzly Industrial.

Christmas Elk Canada

John Adams and Jerry Tierney Have Left the Range…
I also want to say a word in remembrance of two good men (and talented shooters) who really helped the site. John Adams, one of the site’s first Forum members, and a great supporter of our efforts, passed away just over a year ago. And we lost Jerry Tierney, a champion shooter in many disciplines, just this month. These men both served as mentors to me, and their knowledge (and good fellowship) will be missed. John and Jerry — rest in peace, my friends.

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