Sectional Density
Definition
A bullet's mass divided by the square of its diameter (in consistent units). A component of BC; higher sectional density generally produces higher BC for a given drag form.
- Formula
- Bullet mass divided by diameter squared
- Role
- Component of ballistic coefficient (BC)
- Effect
- Higher sectional density raises BC for a given drag form
Common questions
Why does sectional density affect ballistic coefficient rather than being the same thing?+
BC also depends on the bullet's shape, which sets its drag form; sectional density only captures how much mass is packed behind a given frontal area, so two bullets with equal sectional density can still have different BCs if their profiles differ.
Does a higher sectional density always mean a flatter trajectory?+
Generally yes for a given caliber and shape, because a bullet that resists air drag better retains velocity further downrange, but the practical effect also depends on the muzzle velocity and the shooting distance.
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...
- 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;...
- 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....
- 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...