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View Full Version : Rotation of the Earth: Affects on External Ballistics


wildcard
04-07-2008, 12:49 PM
We've all heard of it now either from the movies or people quoting the movies, but does it really effect external ballistics enough for us to worry about even if we're shooting up to 2000 yds?

Certainly the Coriolis effect comes into play on long range projectiles(traveling many miles), but does it actually effect long range rifle shooting? I mean even assuming you were able to calculate wind and atmospheric conditions perfectly, what is the MAXIMUM influence of the rotation of the earth.

I say MAXIMUM because it will vary depending on which direction you are shooting relative to the earth's axis.

hoffmang
04-07-2008, 1:30 PM
You're forgetting about relativity and relative motion. You are in motion from the point of view of someone standing on the moon when you fire regardless of direction fired. The only marginal impact that the earths rotation has on a shot fired in the atmosphere is the movement of the atmosphere being relatively caused by the spin of the earth (windage.)

-Gene

Prc329
04-07-2008, 1:31 PM
According to Mack on Futureweapons it does :)

wildcard
04-07-2008, 1:41 PM
You're forgetting about relativity and relative motion. You are in motion from the point of view of someone standing on the moon when you fire regardless of direction fired. The only marginal impact that the earths rotation has on a shot fired in the atmosphere is the movement of the atmosphere being relatively caused by the spin of the earth (windage.)

-Gene

I understand this point. From a stationary point in outer space, the projectile would appear to move in a striaght line, but for a person on the surface the projectile will appear to be moving in a curvalinear motion across the surface (depending on direction). But does this simply translate into wind? Or is there more to it?

Timberwolf
04-07-2008, 1:54 PM
At the operative distances of the small arms we use (say 1K or less) there would be very little, if any, impact on POA/POI caused by the Coriolis effect. This normally comes into play (IIRC) at distances exceeding 1200 - 1300 (ergo 338 LM and 408 Chey Tac).

What does effect trajectory and be accounted for normally at distances exceeding 600, in normal 30 cal applications, beyond the normal atmospheric conditions, is compensation for the effects of bullet yaw caused by the rifling twist.

Ever notice how long range shooting is similar to being in the arty . . .

wildcard
04-07-2008, 2:09 PM
Don't laugh.. I just learned a ton reading this: http://en.wikipedia.org/wiki/External_ballistics

Now if I could just figure out "how much" these factors actually effect the projectile and i'll be happy.

wildcard
04-07-2008, 2:20 PM
Not that I have seen the formula for it, but it looks like the affects can be ROUGHLY calculated by simply knowing the speed the earth rotates at the target and the time it takes for a projectile to reach the target. This will then change depending on the angle you will be shooting at. Sigh.. too much to think about. It's rather quite similar to shooting a moving target.

hoffmang
04-07-2008, 2:29 PM
Varying gravity due to core density of the earth above which the projectile flies is going to have more (and harder to calculate) effects on the shot than any other motion past wind.

-Gene

Vu 308
04-07-2008, 3:12 PM
Ask marky Mark.

wildcard
04-07-2008, 3:15 PM
Ask marky Mark.

Sadly, that's the first time I heard of it. Then i started hearing other people quote it and decided to do some fact checking. To top it off, my girlfriend told me about the "Coriolis" effect as I was talking about it even though I'm the one with the physics background. It has been an embarassing journey..

EastBayRidge
04-07-2008, 3:18 PM
Snipers Hide had longish threads on the topic here (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Board=5&Number=379231&Searchpage=1&Main=29318&Words=coriolis&topic=0&Search=true#Post379231) and here (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=288504&fpart=1).

rksimple
04-07-2008, 3:24 PM
The SH threads were good. Some funny stuff in there.

wildcard
04-07-2008, 3:31 PM
Snipers Hide had longish threads on the topic here (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Board=5&Number=379231&Searchpage=1&Main=29318&Words=coriolis&topic=0&Search=true#Post379231) and here (http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=288504&fpart=1).

I just read through the threads and there is one thing that everyone seems to be forgetting, even though the effect is maximized when shooting N and S, the further you are from the equator, the less the effect is going to be. In fact, if your targets were at the north and south poles (the ends of the axis), there would be no coriolis effect because the targets would be stationary (though rotating).

Or maybe i'm wrong?

Prc329
04-07-2008, 3:35 PM
I was just messing around with the Mack comment. I do believe it is something that most of us will never encounter. It is hard enough to shoot 1000 yards in CA. Shooting long enough to see the Coriolis effect is banned by name.

PistolPete75
04-07-2008, 4:57 PM
didn't this come out of the movie shooters with marky mark?

Vu 308
04-07-2008, 6:14 PM
No....the movie just made it more known.

This type of thing only matters at EXTREME long ranges in my opinion.

The wind and other factors will kick ur arse before this will.

Got my arse handed to me this weekend by the wind...doubt the rotation of the earth did much at 1K to me. LOL

ar15barrels
04-07-2008, 9:02 PM
According to Mack on Futureweapons it does :)

<whisper>be vewy vewy quiet, I'm hunting wabbits at 1600yds with this 416 barrett.</whisper>