Coriolis Effect on Long-Range Shooting

Capture

While most shooters keep their shots well under 500 yards, extreme long-range shooters are well-versed in the myriad of variables that come into play putting lead on target out to and past 1,000 yards. Generally speaking, most shots under 500 yards t only have to account for windage and bullet drop, but past 800 yards things start getting tricky.

Gunwerks has been kind to break-down the Coriolis Effect, which simply put, is the world spinning and the bullet wanting to fly straight. This phenomenon has to be accounted for or bullets will miss by as much as 4″ to the right or left (depending on your hemisphere) if one were at the North Pole.



Nathan S.

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

Nathan can be reached at Nathan.S@TheFirearmBlog.com

The above post is my opinion and does not reflect the views of any company or organization.


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  • iksnilol

    Only 4 inches? Phew, I thought it would be more serious than that.

    Good thing I don’t really plan on shooting past 800 meters with 308. Kinda hard to do now since I don’t have a rifle. :/

    • Some Guy

      For literally anything that isn’t getting first round hits on very small targets at very great distances it is safe to assume that the bullet and target exist in the same reference frame

      • iksnilol

        For something like a rifle that’s true, artillery might be screwed tho.

        Besides, I don’t think I could afford to shoot farther than 1000 meters. Those super long range rigs are expensive and unpractical. I am thinking of buying a sporterized Mauser for dirt cheap and modding it into a good hunting rig/decent long distance rig.

        • Some Guy

          Yeah as with anything the greater the distance the force is applied over the more effect it has. The Coriolis force happens to be very very small so you have to be shooting well outside the range of most (if not all) man portable weapons for it to be worth doing the math on (or as I said if you want to zap a soda can at 2000m with one shot)

    • Bronezhilet

      Well, it’s a really really big thing with artillery. With rifles it’s more or less a case of ‘oh shucks, I missed by a few inches’. With artillery it can be a ‘whoops, we shot our own dudes’. If I remember correctly you will miss your target by around a full kilometer when shooting at 40 km. Its even funnier when you’re not shooting exactly north/east/south/west. If you don’t take your position on earth (!) and firing direction into account, it appears that the shots fly all over the place.

    • USMC03Vet

      What happened to your rifle? Did it go to university?

      • iksnilol

        I don’t have one in Norway. For competition and target use I borrow a Sauer 200.

        In Bosnia I know a guy who knows a guy (for legal reasons).

  • Vitsaus

    Don’t forget to factor in the position of Mars and the direction of the tides.

    • iksnilol

      Or the horoscope and the mood of the gods.

      • JoelC

        I, personally, prefer to always take the auspices and examine the entrails of sacred chickens before I make long distance shots…

        • iksnilol

          Sacred chickens? I prefer sacred goats but whatever works for ya.

      • RICH

        ….THE INCOMING AND OUTGOING TIDES ALSO HAVE A LARGE EFFECT ON THE PLACIAL DIRECTION OF IMPACT….

  • Bill

    Then factor in altitude, barometric pressure, up/down slope, wind, and temperature. I’m still not impressed when someone gets a hit at a thousand yards after 20 shots, it’s the guy or gal who can sort all that out and do it on the first shot that I want to hang with.

    • If you want to do it with one shot make sure nobody else has been messing with your rifle!

    • eriky

      Well for me it wouldn’t have te be the first one but they do have to repeat it a few shots in a row.

      • Bill

        Good point, that would prove it also. I’m being a little unrealistic in demanding a cold-bore first round hit – a lot can happen in the time of travel for a bullet at that distance – I just don’t like the idea of machine-gunning a bunch of rounds at a target, of course it’ll eventually get hit.

  • The_Champ

    Pretty interesting.

    And yet another reason in my books why hunters trying to make crazy long range shots is inhumane.

    • lucusloc

      If they can do it then I see no problem with it. I know guys for which a 100 yard shot would be inhumane, because they cannot be counted on to make the shot. Hunt to your skill level, not beyond. It is your responsibility to know you skill level, and no one else. The corollary to that is don’t judge others, unless you can offer proof that they exceeded their skill level.

  • smartacus

    soundz like a made-up name, Corey Olis

    • tazman66gt

      was half awake when I first read the title and thought it said clitoris effect.

  • gunsandrockets

    Heh heh, putting on my spacer hat and rubbing my hands together. Let’s go!

    There is a lot wrong spoken and written here.

    The effect spoken of in the video is true, shooting due West vs due East makes a significant change in bullet drop. But the effect is not caused because “the bullet is not spinning with the Earth”, the truth is exactly the opposite of that claim. In addition the effect described is greater the closer the shooter is to the equator of Earth, and has no effect if the shooter is firing from the north or south pole. In fact I think (though I could be wrong) that the “Coriolis effect” describes a different kind of factor than the bullet drop described in the video!

    Here is what is really going on (and it’s the same reason why the preferred launch site for space rockets is close to the equator and the preferred launch direction is towards the East).

    Bullet drop is caused by the interaction of flight time vs gravity. All objects resting on the surface of the Earth are also spinning the same speed as the surface of the Earth, including any bullet ready for firing in a rifle barrel. The Earth spins towards the East, rotating on the axis which passes through the North and South poles. At the surface of the Earth, the speed of this rotation at the Equator (relative to the axis of rotation) is roughly 1,000 mph or 1,500 fps! At the surface of the Earth the speed of this rotation at the Pole (relative to the axis of rotation) is zero.

    So if you shoot a .308 due East while standing on the Equator of the Earth, the bullet leaves the barrel at roughly 2,700 fps. But relative to the gravity of the Earth, that bullet is moving at an effective velocity closer to 4,200 fps. Now the same shooter fires due West. The bullet leaves the barrel at 2,700 fps, but relative to the gravity of the Earth that bullet is only moving at an effective velocity of 1,200 fps!

    Here is a fun experiment for someone who lives close to the Equator. Take a firearm with a measured muzzle velocity of about 1,500 fps (or 450 ms), shoot it due West and measure the bullet drop over distance. Should prove freaky.

    • Bill

      I think you’re on to something, but it would also apply equally to rounds being fired in circumpolar directions. Rounds will strike East or West if they are being fired North or South, and depending on which hemisphere they are fired from. (and I thought a year’s worth of an astronomy class would be useless, as it has been for the last 30 years).

      We need to page someone from NASA Orbital Mechanics, and they can start off with the “water swirling down a drain in the Northern and Southern hemispheres” lecture.

      • BinaryWatcher

        You got one, right here. (I wasn’t directly in the orbital mechanics section, but given my graduate work in binary stars, I could do the work. And I worked side by side with ’em.) Had a friend point me at this conversation from Faceplant, uh, I mean Facebook.

        Gunsandrockets pretty much has it correct; this is exactly why, to put a craft into a nominal posigrade orbit, we launch at low latitudes going east. It adds nearly the full 1000mph of the Earth’s rotation to the rocket’s insertion velocity. It’s also why we have launch facilities on the WEST coast for other types of orbits, including retrograde and polar. The whole science of non-continuously-accelerated projectiles is known as ballistics, whether it’s a rocket, a bullet, or a thrown ball, and the projectiles that don’t go into orbit will tend to follow near-parabolic trajectories. (They’d be elongated ellipses with one focus at the Earth’s center of mass, if the Earth wasn’t actually there.)

        Firing from a circumpolar direction gets very complicated very fast. Pretty much, if you’re close enough to the pole, anything you fire is going to be defined as “away from the pole” and hence south (from the north pole) or north (from the south pole). And yes, you would get some very serious coriolis effects.

        • Bill

          Now on to red shift / blue shift 😉

          • BinaryWatcher

            Sorry! Not applicable. Gotta be moving bleeping fast to have any Doppler shifting of light.

  • quraina

    Thanks! Now I understand it much better than before.

  • Dolphy

    Wow, and this used to be a joke in the COD community.