Q: Can you explain what the Coreolis Acceleration of a projectile is all about? I believe it has something to do with whether the direction of the rifling twist is right-hand or left-hand. I know most modern rifles have a righthand twist.
A: A projectile fired in the Northern Hemisphere has a Coriolis Acceleration (C.A) drift to the right, while in the Southern Hemisphere it is to the left. The formula is: Earth rotation rate (0.0000729 degrees per second), times double the projectile velocity (fps), times the SIN (latitude), plus for Northern and minus for Southern. Now consider the projectile gyroscopic drift,
which is to the right with a right-hand rifling twist and left with a left-hand twist. As you can see, if the rifling was given a left-hand twist for Northern latitudes, it would somewhat correct for C.A drift. By the way C.A drift is approximately one inch at 700 yards for a .30-06 projectile. This is critical for accuracy with long-range naval guns such as the 16-inchers on the battleships and is in fact figured into the ballistic computers on board the ships. As far as your average hunting rifle is concerned, just set your sights to compensate for both.