Coriolis Effect

The Coriolis effect is an apparent deflection of moving objects from a straight path when they are viewed from a rotating frame of reference. In layman's terms, it means that long range fire (artillery shells and sniper rounds) will not appear to fly in a straight line from the shooter to the target because of the rotation of the Earth on its axis. Rather, the round or shell will appear to curve.In actuality, the shot is flying in a straight line but the turn of the Earth moves the target so it will look as if the round or shell is curving. Artillery gunners and snipers are well-trained to compensate for the Coriolis effect by actually not aiming directly at their target, but off to the side so that by the time the bullet makes it to the target distance, it has "curved" to hit thetarget.

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 offlight, 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'tmeasure 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 onheavier/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").

Serious long range shooters will zerotheir windage at a long distance (say 800yds), this will split the effect and cause closer shots to hit slightly left (assuming northern hemisphere) and further shots to hit slightly to the right. This limits the impact of CE and SD to the point of being able to ignore them, except for very extreme range shooting (in which nothing can be ignored). Extreme range shooting (2000yds +), is typically donewith the aid of PDA's and/or Laptop computers.

The real trick to hitting something at long range, is judging the wind correctly. For hunters and snipers, judging the wind is the toughest part of making a long distance shot.

The Coriolis Effect has commonly been accused of affecting everything from the flight of baseballs thrown by left-handed pitchers to the direction the water spins in thetoilet. All of these (including the effect on sniper fire) are simply urban legends.

The Coriolis Effect is caused by the fact that objects near the equator are moving faster around the axis of the earth than objects at the poles. So if I were to stand at the North Pole and fire an ICBM directly at Ecuador, then if I neglect air resistance, I would miss Ecuador because my missile would be flyingdirectly South, and, being separated from the earth below, my bullet wouldn't pick up any of the rotational velocity of the earth. Ecuador, meanwhile, would be moving around the axis of the earth at about 1000 mph, and given how far of a shot that is, would be well out of the way of my ICBM by the time it got there.

By the same token, if I were standing in Ecuador and shot my ICBM directly north...