Spin Drift
Definition
Consistent lateral drift of a bullet in the direction of rifling twist, caused by gyroscopic precession of the bullet's nose around the velocity vector. For right-hand twist, drift is always to the right, regardless of hemisphere.
- Field
- Forensic ballistics, long-range trajectory analysis
- Cause
- Gyroscopic precession of the bullet around the velocity vector
- Right-hand twist direction
- Drift to the right
- Independent of
- Hemisphere
Common questions
How does spin drift differ from wind drift in a trajectory reconstruction?+
Spin drift is a consistent, predictable lateral shift caused by the bullet's own rotation and rifling twist, while wind drift depends on external crosswind conditions at the time of the shot, so the two are calculated and applied separately.
Why does spin drift matter more at long range than at short range?+
The lateral displacement accumulates with time of flight, so it is negligible at close range but can become a measurable factor in reconstructing bullet path or point of origin at extended distances.
Related terms
- 4DOF Model
- A four-degree-of-freedom ballistic model that adds aerodynamic pitch and yaw to the standard 2DOF (gravity + drag) model, accounting for spin drift...
- BDC (Bullet Drop Compensator)
- Elevation turret or reticle markings that encode the required elevation correction for a specific load at preset ranges. Allows rapid correction without...
- Coriolis Effect
- Apparent deflection of a moving body due to the rotation of the Earth. In the Northern Hemisphere, deflects projectiles to the right...
- Eötvös Effect
- The vertical component of the Coriolis effect on a bullet. Increases impact elevation for eastward-fired shots, decreases it for westward-fired shots. Typically...
- Fire Control System (FCS)
- An integrated optic, rangefinder, and ballistic solver that computes and displays a real-time firing solution. Examples: TrackingPoint PGF, Elbit FALCON, Rafael MARS....
- Laser Rangefinder (LRF)
- A device that measures range by timing the return of a laser pulse from the target. Typical accuracy: plus or minus 1...
- Magnus Effect
- A force on a spinning body in a crosswind perpendicular to both the spin axis and the crosswind direction. Produces a vertical...
- Miliradian (Mil)
- 1/1000 of a radian. Equal to 10 cm at 100 m, 1 m at 1,000 m. Used as the angular unit in...
- MOA (Minute of Angle)
- 1/60 of a degree of arc. Equal to approximately 2.908 cm (1.047 inches) at 100 m. Used in civilian and some law...