Spin Drift: Calculation
Equation
To manually estimate spin drift, we only need to know the distance of our shot and how long our bullet will be in flight.
((SG * Time of Flight ^ 1.83) / Distance) * 1000 = Spin Drift in MRADs
The variable “SG” is the stability factor of our projectile, considering many details of rifle and bullet construction. This information will be provided for commonly used rifle and bullet combinations in a chart below.
Data Collection
Time of flight can be found in the ATragMX under the “RC” button in the top right of the screen or derived in an online ballistics program. As the ATragMX suite is not available in situations where manual ballistics are relevant, time of flight information should be recorded prior to operation start.
Stability factor or SG is provided below for common combinations of rifles and projectiles for campaigns that utilize manual ballistics. Note that the following SG values have been further modified to simplify the initial equation:
| Rifle | Twist Direction | Projectile | Modified SG |
|---|---|---|---|
| M24 SWS | Right | M118LR | .0759 |
| M24 SWS | Right | M62 Tracer | pending |
| M24 SWS | Right | M993 AP | pending |
Calculation Example
Sgt McShooty is deployed as a Spotter (Manual) on a Honeybadger. He ranges a priority target at 900m, a shot that will have a time of flight of 1.8s. His sniper is using M118LR ammunition for this shot.
((.0759 * 1.8 ^ 1.83) / 900) * 1000 = .25 MRADs
Because the rifiling of the M24 SWS barrel twists to the right, the bullet will deflect .25 MRADs to the right due to spin drift.
