AR15.Com Archives
 Coriolis Effect and Bullets?
ampn  [Team Member]
8/20/2007 8:03:44 PM EST

Does the rotation of the earth cause bullet drift at long range (1000 yards and longer)?
If so, how much?

Google isn't giving me a straight answer. What do you think?

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MisterWilson  [Team Member]
8/20/2007 8:06:28 PM EST
I think that the movie "Shooter" was full of shit and chock full of flaws that any respectable "firearms consultant" should have caught.
ampn  [Team Member]
8/20/2007 8:08:15 PM EST
I remember a discussion on a long range forum talking about this subject and this was before that crappy movie came out.
Keith_J  [Team Member]
8/20/2007 8:08:35 PM EST
Time of flight is far too short and the resultant distance traveled makes it all but trivial for any rifle you can shoulder.

Now arty and the like DO have significant effects. But not anything you want to fire.
StealthyBlagga  [Member]
8/20/2007 8:15:29 PM EST
Its a well-known fact that your barrel needs a right-hand twist if you are in the northern hemisphere, and a left-hand twist if you are in the southern hemisphere .
Keith_J  [Team Member]
8/20/2007 8:16:34 PM EST
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .357 MOA.


MisterWilson  [Team Member]
8/20/2007 8:20:23 PM EST

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.




Foot. Meet mouth.
USGI_45  [Team Member]
8/20/2007 8:21:52 PM EST

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.





3 inches at 1000 yards? 6+ inches at 2k yards. If I were a sniper I would adjust for that
Keith_J  [Team Member]
8/20/2007 8:22:10 PM EST

Originally Posted By MisterWilson:

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.




Foot. Meet mouth.



[Geico Caveman]What?[/Geico Caveman]
ampn  [Team Member]
8/20/2007 8:22:19 PM EST
I went to a public school, so forgive me!

How does this happen if the Earth's atmosphere is rotating at the same rate as the surface?
Keith_J  [Team Member]
8/20/2007 8:23:03 PM EST

Originally Posted By USGI_45:

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.





3 inches at 1000 yards? 6+ inches at 2k yards. If I were a sniper I would adjust for that


You don't shoot at 1000 yards, do you?

jfrankparnell  [Member]
8/20/2007 8:25:01 PM EST
what if it passes over a conveyer belt that is spinning in the opposite direction of the bullet rotation?
Keith_J  [Team Member]
8/20/2007 8:26:46 PM EST

Originally Posted By ampn:
I went to a public school, so forgive me!

How does this happen if the Earth's atmosphere is rotating at the same rate as the surface?


It isn't wind. It is VELOCITY. Get youself a tennis ball and go experiment at the local merry-go-round. Have your lovely assistant spin the MGR while you are standing at the center. Spin it fast. Throw the ball at a target on the edge of the MGR.

That is why I used the example location of the North Pole as the firing position with the greatest effect because the shooter is not moving with any lateral velocity while a target positioned south of the North Pole would have some lateral velocity.

Shooting due east or west has no effect as there is no lateral velocity difference.

Keith_J  [Team Member]
8/20/2007 8:28:48 PM EST

Originally Posted By jfrankparnell:
what if it passes over a conveyer belt that is spinning in the opposite direction of the bullet rotation?


The airplane takes off.
Grunteled  [Team Member]
8/20/2007 8:35:39 PM EST
My question would be how would it ever really be a factor? If my target and I were even 2000 yards apart we are both already moving at the rotational speed of the earth minus any tiny difference based on lower latitude. So is the rifle and the bullet. The bullet would be moving at that rate when it left the barrel.
USGI_45  [Team Member]
8/20/2007 8:41:20 PM EST

Originally Posted By Keith_J:

Originally Posted By USGI_45:

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.





3 inches at 1000 yards? 6+ inches at 2k yards. If I were a sniper I would adjust for that


You don't shoot at 1000 yards, do you?




No, thats why I said if I were a sniper. Whats the longest confirmed kill. Like 2500+ yards
HoodyHoo21  [Member]
8/20/2007 8:45:26 PM EST
I know they take it into account when firing artillery, but the time of flight is much greater then any bullets.
MisterWilson  [Team Member]
8/20/2007 8:45:27 PM EST

Originally Posted By USGI_45:

Originally Posted By Keith_J:

Originally Posted By USGI_45:

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .374 MOA.





3 inches at 1000 yards? 6+ inches at 2k yards. If I were a sniper I would adjust for that


You don't shoot at 1000 yards, do you?




No, thats why I said if I were a sniper. Whats the longest confirmed kill. Like 2500+ yards


"That's because desk jockey pogues don't usually like going to the places it takes to confirm them"

Keith_J  [Team Member]
8/20/2007 8:46:01 PM EST

Originally Posted By Grunteled:
My question would be how would it ever really be a factor? If my target and I were even 2000 yards apart we are both already moving at the rotational speed of the earth minus any tiny difference based on lower latitude. So is the rifle and the bullet. The bullet would be moving at that rate when it left the barrel.


The lateral valocity difference is highest at the higher latitudes as it is a sine function of lattitude. And it is maximum when the firing axis is due north or south.

Shooting 16" naval guns at a target 25 miles distant has significance. But for even snipers, it is a WASH compared to wind, mirage, humidity, temperature and atmospheric pressure.
FrankSymptoms  [Team Member]
8/20/2007 8:57:05 PM EST

Originally Posted By Keith_J:
Time of flight is far too short and the resultant distance traveled makes it all but trivial for any rifle you can shoulder.

Now arty and the like DO have significant effects. But not anything you want to fire.


Yup. When you get to ranges of, say, five miles or so, then the earth's spin must be accounted for.


Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .357 MOA.




That is .357 MOA. Which is less than the diameter of the bullet.

But it gets even more complex than that. At 1000 yards, even shooting straight north or south, you are for all intents and purposes at the same latitude. In other words, the difference between your speed west-to-east and the target's is virtually zero.
Grunteled  [Team Member]
8/20/2007 8:57:52 PM EST

Originally Posted By Keith_J:

Originally Posted By Grunteled:
My question would be how would it ever really be a factor? If my target and I were even 2000 yards apart we are both already moving at the rotational speed of the earth minus any tiny difference based on lower latitude. So is the rifle and the bullet. The bullet would be moving at that rate when it left the barrel.


The lateral valocity difference is highest at the higher latitudes as it is a sine function of lattitude. And it is maximum when the firing axis is due north or south.

Shooting 16" naval guns at a target 25 miles distant has significance. But for even snipers, it is a WASH compared to wind, mirage, humidity, temperature and atmospheric pressure.


I get your example.... just hard to picture anyone trying to paint it as a factor in real-world shooting.
prk  [Member]
8/20/2007 9:03:05 PM EST
Keith_J is right. It's a factor in long range really big bore fire, but over CF range, other things overshadow it. The same MIGHT be said for the effect of powder temperature.

Speaking of that, I remember ambient temperature (re powder) being part of the GFCS, but don't recall anything about the temperature of the gun.
Keith_J  [Team Member]
8/20/2007 9:07:31 PM EST

Originally Posted By FrankSymptoms:

Originally Posted By Keith_J:
Time of flight is far too short and the resultant distance traveled makes it all but trivial for any rifle you can shoulder.

Now arty and the like DO have significant effects. But not anything you want to fire.


Yup. When you get to ranges of, say, five miles or so, then the earth's spin must be accounted for.


Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .357 MOA.




That is .357 MOA. Which is less than the diameter of the bullet.

But it gets even more complex than that. At 1000 yards, even shooting straight north or south, you are for all intents and purposes at the same latitude. In other words, the difference between your speed west-to-east and the target's is virtually zero.


Yes, I corrected my MOA calculation...and we were talking about 1000 yards. And I used the absurd case of the shooter being at the North Pole and the target somewhere to the south. You are correct, most normal situations would be much less than .1 MOA. Unless we are talking SATELLITES!
blackjack333  [Member]
8/20/2007 10:18:04 PM EST
read this..

the Paris gun
CletusRoundbelly  [Team Member]
8/20/2007 10:38:09 PM EST

Originally Posted By Keith_J:
Do the math yourself. Consider a .50 BMG averaging 2100 FPS over that 1000 yard range. Fired due south, at the north pole, for maximum effect. Lateral velocity of the bullet at time if firing is zero.
The target is moving at the rate of one revolution per 24 hours. Or it travels 2000*pi yards in 24 hours. That is its lateral velocity. 0.073 yards per second. About 2.6 inches per second.

So the bullet takes 1.43 seconds to make the 1000 yards. The target moves 3.74 inches. That is .357 MOA.





Hey! try to keep it realz in here! don't be cornfusing us with all your book learnin and math and shit.


Hey look, a squirrel!


< runs off >
trg42  [Member]
8/21/2007 4:59:45 AM EST
Coriolis effect is negligable at short ( non artillary ) ranges

http://www.nennstiel-ruprecht.de/bullfly/coriolf.htm#header

Magnus effect and Magnus force has more significant but still relatively tiny effect

http://www.nennstiel-ruprecht.de/bullfly/fig9.htm

http://www.nennstiel-ruprecht.de/bullfly/fig10.htm

We shoot 338 Lapua and 50bmg at 1000+ and wind / altitude and accuracy of rifle has way more effect that the last thing I think about are the coriolis / mangus etc

Food for though - if you have a 3/4 MOA rifle @100 you are most likely no better than 10" at 1000yrds ( generally more because of wind etc ) so why worry about these tiny theoretical effects

warped  [Member]
8/21/2007 5:22:18 AM EST

Originally Posted By Keith_J:

Originally Posted By ampn:
I went to a public school, so forgive me!

How does this happen if the Earth's atmosphere is rotating at the same rate as the surface?


It isn't wind. It is VELOCITY. Get youself a tennis ball and go experiment at the local merry-go-round. Have your lovely assistant spin the MGR while you are standing at the center. Spin it fast. Throw the ball at a target on the edge of the MGR.

That is why I used the example location of the North Pole as the firing position with the greatest effect because the shooter is not moving with any lateral velocity while a target positioned south of the North Pole would have some lateral velocity.

Shooting due east or west has no effect as there is no lateral velocity difference.



These studies have been done most recently by Professor John Kallend of IIT, he is a world renowned physicist, he can explain to you very simply that the coriolis effect does not have enough influence on projectiles traveling such a short distance.

However in the case of ARTY the distance traveled is such that the effect comes into play.

He also did a few other DoD studies that were quite interesting.

The man is like Mythbusters, only extremely educated.
warped  [Member]
8/21/2007 5:36:55 AM EST
It does have an effect on artillery - easily calculated, "even a caveman can do it". For "Big Bertha" in WWI the Coriolis effect shifted the aiming point about a mile, in accordance with the calculation (at the latitudes in question, Paris is moving about 7mph slower than the Belgian border where the gun was fired. The shell's flight time was around 10 minutes, so Paris moved about a mile relative to the gun during the shell's flight).

And there was a Coriolis problem at the Battle of the Falkland Islands in 1914.

According to NASA

"The effects of the Coriolis Force must be considered for things that move relative to the Earth, especially at the higher latitudes of both hemispheres. For example, in World War I, during a naval battle near the Falkland Islands (off the east coast of South America, about 52 degrees south latitude) between the German and British Navy, British gunners were surprised to see their salvos falling 100 yards to the left of the German ships. The engineers who designed the sighting mechanisms were well aware of the Coriolis deflection and had carefully considered it, however, they neglected the fact that not all sea battles occur in the Northern Hemisphere. Thus, during the engagement, the initial British shots fell at a distance from the targets equal to twice the Coriolis deflection."
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