4DOF Model
Definition
A four-degree-of-freedom ballistic model that adds aerodynamic pitch and yaw to the standard 2DOF (gravity + drag) model, accounting for spin drift and Magnus effect. Hornady 4DOF is the most widely accessible implementation; ENFSI recommends 4DOF or higher for forensic reconstruction beyond 1,000 m.
- Adds to base model
- Aerodynamic pitch and yaw
- Effects captured
- Spin drift and Magnus effect
- Common software
- Hornady 4DOF
- Recommended for
- ENFSI: reconstructions beyond 1,000 m
Common questions
How is a 4DOF model different from the simpler 2DOF model?+
A 2DOF model only accounts for gravity and drag acting on the bullet's path. A 4DOF model adds two rotational degrees of freedom so it can also predict spin drift and the Magnus effect, both of which matter once range gets long.
When would a reconstructionist actually need a 4DOF model?+
For close and moderate range shots a 2DOF model is usually accurate enough. A 4DOF model becomes important for long-range trajectory reconstruction, where spin-induced drift can shift point of impact by a meaningful margin.
Related terms
- 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...
- Spin Drift
- Consistent lateral drift of a bullet in the direction of rifling twist, caused by gyroscopic precession of the bullet's nose around the...