Drag Coefficient (C_D)
Definition
A dimensionless number characterising the aerodynamic drag force relative to the dynamic pressure and the projectile's cross-sectional area. Varies with Mach number; peaks near Mach 1 in the transonic regime.
- Symbol
- C_D
- Type
- Dimensionless number
- Depends on
- Mach number, cross-sectional area, dynamic pressure
- Peak region
- Near Mach 1, transonic regime
Common questions
Why does drag coefficient matter for a ballistic trajectory reconstruction?+
C_D determines how quickly a bullet decelerates in flight, which directly affects the drop, time of flight, and terminal velocity used in a shooting reconstruction. Using a fixed C_D value across the whole trajectory, rather than accounting for its rise near Mach 1, can produce a meaningfully wrong distance or angle estimate for long-range shots.
How does a ballistic coefficient relate to the drag coefficient?+
Ballistic coefficient is a practical shooting figure that combines the projectile's mass, cross-sectional area, and a reference drag model into one number, letting shooters and analysts compare how well different bullets resist deceleration without recalculating the underlying C_D curve for each one.
Related terms
- Aerodynamic Drag
- The retarding force exerted by air on a moving projectile. Proportional to air density, the square of velocity, the drag coefficient, and...
- Ballistic Coefficient (BC)
- The ratio of a projectile's sectional density to its drag relative to a reference standard (G1 or G7). Higher BC means less...
- G1 Drag Standard
- The Gavre Commission reference projectile: flat base, round-nose ogive. Established in the late 19th century and codified at Aberdeen Proving Ground. Standard...
- G7 Drag Standard
- A long, boat-tailed secant-ogive reference projectile developed by Bryan Litz at Applied Ballistics. More accurate for modern spitzer-BT precision and military rifle...
- Hatcher Rule
- A simplified wind-drift estimation formula from Major General Julian Hatcher's Hatcher's Notebook (1947). Useful as a field check and courtroom cross-reference; diverges...
- Litz Wind Drift Model
- The velocity-integrated wind-drift calculation method from Brian Litz's Applied Ballistics for Long Range Shooting (2015), implemented in AB Quantum and Hornady 4DOF....
- Sectional Density
- A bullet's mass divided by the square of its diameter (in consistent units). A component of BC; higher sectional density generally produces...
- Transonic Regime
- The velocity range from approximately Mach 0.8 to 1.2 (272 to 408 m/s at sea level, 15 degrees C). Wave drag peaks...
- Wind Drift
- Lateral deflection of a bullet by a crosswind component. Grows with time-of-flight (faster than range) and is the most variable error source...