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Coriolis Effect - Marketing VS Reality

13K views 60 replies 24 participants last post by  Orkan 
#1 · (Edited)


I've seen this video thrown around quite a lot lately. Great marketing.

Yet I'm left with the question: Why haven't I been able to observe Coriolis effect when I'm shooting?

I consider myself a good shooter. Others consider me an outstanding shooter. Most days I'm 1/4moa or better. I have the best equipment money can buy, and spend more time shooting than nearly anyone I know. I have cartridges ranging from 22lr all the way to 375CT. I shoot at distances of up to 3000yds. I spend a ton of time between 1000 and 2000yds. Yet I have never experienced a need to compute for coriolis effect.

Spin drift was something that I encountered that absolutely affected my shots as I went beyond 500yds. It's easy to see and easy to prove. If you're out shooting at 1000yds and you have a solid firing solution in your ballistic computer that is matching perfectly with your dope... switch spin drift off, and see what happens. All of a sudden you'll be a tenth of a mil or so off. This can be practiced on very calm days, and the effects will be pretty easily proven if there are enough good shooters with good rifles around. If a guy can't shoot POA/POI consistently, well then all bets are off, as spin drift can be hidden behind a 1moa shooter pretty easily.

Coriolis on the other hand has never surfaced in my shooting as something I needed to account for. I have deer killed out to 1000yds and I was shooting all manner of directions, and never once had something go awry that could be attributed to coriolis.

I like gunwerks. I think they've built a great company and they have championed some very good things. Long range hunting in general, the 7LRM cartridge, as well as pressed forward a lot of other tech. However, I think there should be a little bit of humility displayed in some cases. I am willing to bet if they replicated that test a dozen times, they would get different results each time. It is noteworthy that I have several rifles which I have proofed out completely to 1000yds, all of which I can generate a firing solution and make center mass impacts, but none of which use firing solutions computed with coriolis accounted for.

My main point of contention on the subject is that most advocates of coriolis simply say that the bullet leaves the ground at one point, impacts at another, and while it is detached, the earth is spinning beneath it... causing the target to move out of alignment with the bullets path. There is one big flaw with this theory: The atmosphere is spinning with us. The closer to the ground you are, the more the atmosphere is being drug along. We are also spinning with it. If these two things were not true, every time you jumped up off the ground you'd get slammed into the wall at 1000mph. I talked to an old artillery gunner one time about the subject... and he agreed with me that it was an effect that was totally lost in the noise. They didn't compute for it. So if an artillery shell which is shooting at a target a few miles away doesn't need to compute coriolis, do we as long range shooters?

There are not many topics regarding shooting which I feel that I don't have a good lock on, but this is one of them. There are folks talking about coriolis as if it settled regarding its effect on shooting, but I don't feel that it is at all settled. Might not have it resolved in my lifetime... who knows. Yet I'm not willing to just accept things at face value because I watched a video, and I don't think anyone else should either.

Do you compute for coriolis?
 
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#43 ·
Sort of like how the USSR "dissolved" shortly after they got to see how badly their battlefield weapons, expecially the heavy armor, fair'd in the First Gulf War. I believe the only "friendly" armored vehicle lost in the battle of 73 Easting was a Bradley. Compare this to the 160 tanks, 180 personnel carriers, 12 artillery pieces and more than 80 wheeled vehicles, along with several anti-aircraft artillery systems that the Republican Guard lost.
 
#47 ·
I'm pretty sure the USSR dissolved because they went bankrupt spending 10 years in Afghanistan. As far as Iraqi armor, it was as basically junk. T55s, t64s,type69s, old bmps, old zsus, old brdms. They had that stuff In great numbers. Direct fire not withstanding, a fair amount of the battle damage was inflicted by close air support and indirect fire. We did lose a few tanks due to friendly fire. After that battle they came up with those louvered battle boards you see on tanks nowadays, they show up pretty well in an apache gunners flir.
 
#52 ·
While Hollywood and some shooters have latched onto the Coriolis Effect for the drift of the bullet, and the physics certainly support that it does add a component to External Ballistics, I think many folks (none on this forum of course) have confused this with Spin Drift. For those of you familiar with ladder sights on a 1898 Krag or a 1903 Springfield this component is well established and significant enough to demand compensation. Interestingly, I've never seen an in depth discussion on spin drift, possibly because it is so dependent on bullet caliber, weight, configuration, velocity, etc. etc. Here is what Wikipedia says about Spin Drift.

"Gyroscopic drift is an interaction of the bullet's mass and aerodynamics with the atmosphere that it is flying in. Even in completely calm air, with no sideways air movement at all, a spin-stabilized projectile will experience a spin-induced sideways component. For a right hand (clockwise) direction of rotation this component will always be to the right. For a left hand (counterclockwise) direction of rotation this component will always be to the left. This is because the projectile's longitudinal axis (its axis of rotation) and the direction of the velocity vector of the center of gravity (CG) deviate by a small angle, which is said to be the equilibrium yaw or the yaw of repose. The magnitude of the yaw of repose angle is typically less than 0.5 degree.[35] Since rotating objects react with an angular velocity vector 90 degrees from the applied torque vector the bullet's axis of symmetry moves with a component in the vertical plane and a component in the horizontal plane; for right-handed (clockwise) spinning bullets, the bullet's axis of symmetry deflects to the right and a little bit upward with respect to the direction of the velocity vector as the projectile moves along its ballistic arc. As the result of this small inclination, there is a continuous air stream, which tends to deflect the bullet to the right. Thus the occurrence of the yaw of repose is the reason for the bullet drifting to the right (for right-handed spin) or to the left (for left-handed spin). This means that the bullet is "skidding" sideways at any given moment, and thus experiencing a sideways component.[36][37]"

My background is also in Armor, starting my career as an Armor Gunnery Instructor at Fort Knox in 1972. On the M60A1 (our top line tank at that time) our mechanical computers certainly did adjust for spin drift when shooting HEP, a spinning round. However, not when shooting HEAT, a fin stabilized round. That is the reason the M1A1 doesn't. The gun (not rifle) is a smooth bore design and its rounds are fin, not spin stabilized. The affects of Gyroscopic Drift or Spin Drift are therefore either negligible or nonexistent. Though not a Navy "puke" (apologies to all you Swabbies) I have studied the mechanical computers on the big battle wagons and Spin Drift was in fact one of the components considered in their calculations of External Ballistics, undoubtedly a fixed component.

Don't know how this adds to the conversation but I provide it nonetheless.

Keith Herrington
 
#53 ·
Very interesting. I haven't shot to a range yet where spin drift or coriolis (if it really exists) would affect my rounds outside of my error margin when shooting. Definitely good ideas to keep in mind. Hopefully I'll get the chance to shoot far enough soon to learn about them firsthand.
 
#54 ·
I've attended the Gunsite Extreme Long Range Rifle course three times.
Grinding out computer generated firing solutions I would input zero wind then set my windage to the outputted value so as to "null" my windage for both coriolis and spin-drift.
Then I'd apply a wind hold using my reticle.

It worked pretty well....sort of.....sometimes.
As I've mentioned before missing targets because the laws of probability demand it isn't much fun.
Hitting targets at extreme range is exciting until you realize it's the equivalent of rolling a Yatzi.
 
#56 ·
Same video as started the thread.

So there is an assumption that coriolis only affects east/west shooting vs. north/south. That hurts my head. If Coriolis has a real effect then there should be a eastward drift of the target while the bullet travels if shooting north-south.

If the answer to the above is the force acts so that the shooter, bullet, and target are all moving eastward together and thus no visible effect, then how does that not apply to shooting east-west too?

The same force of the earth turning applies to all three parts (shooter, bullet, target) equally in relation to each other no matter what direction you shoot at the beginning of the shot. What's the mathmatical model to show that once the bullet leaves the barrel the force no longer "pushes" on the bullet.

Maybe I am spewing nonsense but the whole idea of it having an effect shooting east-west vs. north-south doesn't make sense to me.
 
#57 ·
The vertical effect o the bullet fire straight east or west is the Eotvos Effect and is cause by centrifugal forces of the earth rotation to my understanding from what I have read.
On another note if you alway shoot at the range not saying that all ranges are oriented the same but most are oriented south to north.

Cliffy
 
#59 ·
You are quite correct. Since the Coriolis Effect is a constant and easily corrected for on a fixed range, range designers ignore the effect entirely. It would only be a factor (and a small one at that) in an environment where the shooter is shooting in a variety of directions and therefore needs to adjust to minimize or eliminate its effect.

Keith
 
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