Ballistic Coefficient (BC)
Definition
The ratio of a projectile's sectional density to its drag relative to a reference standard (G1 or G7). Higher BC means less velocity loss per unit range. Computed from the ratio of actual drag to the reference drag function.
- Type
- Dimensionless number (ratio)
- Reference standards
- G1 and G7 drag functions
- Key relationship
- Higher BC equals flatter trajectory and less wind drift
Common questions
What does a higher ballistic coefficient mean for a bullet in flight?+
A higher BC means the bullet flies flatter, drifts less in the wind, and keeps more energy as it travels downrange. It overcomes air drag more effectively than a lower BC projectile, so it loses less velocity over distance.
How is ballistic coefficient calculated?+
BC is the ratio of a projectile's sectional density to its drag, compared against a reference standard like G1 or G7. It is a dimensionless number that compares the bullet's actual drag to the reference drag function.
Why do forensic experts care about ballistic coefficient?+
BC helps predict bullet behavior downrange. Understanding how far a bullet travels, how much it drifts in wind, and what velocity it retains are critical for reconstructing shooting scenes and the geometry of bullet flight paths.
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...
- Deflagration
- A subsonic combustion front propagating through an explosive by thermal conduction. Characteristic of low explosives such as black powder and smokeless powder;...
- Drag Coefficient (C_D)
- A dimensionless number characterising the aerodynamic drag force relative to the dynamic pressure and the projectile's cross-sectional area. Varies with Mach number;...
- External Ballistics
- Study of bullet flight from muzzle to target. Governed by gravity, air drag, wind, spin-stabilisation, Magnus effect and (at long range) Coriolis...
- 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...
- Internal Ballistics
- Study of what happens inside the firearm from primer ignition to bullet exit at the muzzle. Includes propellant combustion, gas pressure, bullet...
- 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....
- Permanent Cavity
- The lasting wound channel produced by the bullet's direct crushing and laceration of tissue. Diameter approximates expanded projectile diameter. At handgun velocities,...
- 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...
- Temporary Cavity
- The transient radial tissue displacement produced by a bullet's passing. Caused by the transfer of kinetic energy to surrounding tissue via compression...
Explained in these topics
- Drag, Ballistic Coefficient and Wind DriftThe ratio of a projectile's sectional density to its drag relative to a reference standard (G1 or G7). Higher BC means less velocity loss per unit range. Compu...
- Internal, External and Terminal Ballistics: BasicsDimensionless number describing how well a bullet overcomes air drag. Higher BC means a flatter trajectory, less wind drift and more retained energy downrange.