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Old 23rd September 2010, 12:56 PM
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Mog Mog is offline
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Originally Posted by L-S-R View Post
Would the Coriolis effect of the earth have a different effect on pellets on different hemispheres of the earth? Another spanner and I'll get my coat!
Apparently it does, found the following at makes interesting reading, don't pretend to understand it fully, but I'm sure the rest of you will.

Coriolis Effect :
The formula is:

Fc = -2mω X Vr

Fc = Coriolis force
m = bullet's mass
ω = Eart's angular velocity (of spin)
X = vectorial product
Vr = bullet's velocity

The Coriolis Effect (CE) will typically move a 1000yd shot around .5 moa (Minute of angle) (depends on the distance from the equator). The coriolis effect actually affects all bullets, but is ignored at closer ranges. In the Northern Hemisphere, the effect moves bullets to the right and in the Southern Hemisphere, it moves them to the left. The amount of movement is related to the time of flight, amount of drop and the distance from the equator (further=more). Newton and his cronies were trying to put their finger on this effect hundreds of years ago and actually got pretty close to figuring it out. Newton supposed that anything falling toward the ground, actually should spiral toward the center of the earth (this is actually what the coriolis effect is!). Unfortunately, they couldn't measure it back then.

Another effect that impacts bullet flight is called Spin Drift (SD). SD will move a bullet to the right for barrels with right hand twist rifling and will move it left for barrels with left hand twist rifling (right hand twist is by far the most common). The amount that SD impacts a bullet is related to the amount of drop and the rate of spin (higher spin rates are used on heavier/long range bullets to keep them stable). A typical SD will be .2moa at 1000yds. SD is actually a torque that acts perpendicular to gravity (check out the 'right hand rule' in physics).

SD and CE add together for right hand twist barrels in the northern hemisphere (or left/southern). Their total affect is usually less than 1moa at 1000yds (10.4").

Not a lot over 1000yds but 10" takes you outside the kill zone.
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