Spin drift (or gyroscopic drift) causes the bullet to drift slightly horizontally at long shooting distances. The direction of the drift is the same as the barrel twist rotation, i.e. in your typical right-handed rifle it is in the right hand direction. Spin drift is caused by aerodynamics forcing the bullet tip to turn slightly in the direction of rotation as the bullet tip follows its curved flight path. This rotation of the bullet is very small, usually less than 0.1 degrees, but because it affects the entire flight path, it moves the bullet slightly in the direction of the spin.
The magnitude of the spin drift is most affected by the spin rate, bullet length and flight time (bullet velocity), to a lesser extent also by air density.
The Spin Drift correction can be turned off in the Manage Rifle Cartridge data menu under the current weapon profile (Sight-In settings), but we recommend that you select ‘On’ and then leave it as is. In extreme long range shooting (500 m/yds and up), you can fine-tune the spin drift magnitude to match the exact spin drift tested in practice with your firearm and cartridge combination. However, this precise determination of the actual spin drift is very difficult, because the effect of even a very small wind gust is usually many times larger than the magnitude of the spin drift. Therefore, using the factory setting usually gives the most reliable result.
Our next tip will feature how to build your own reticle. Stay tuned!