How is sectional density calculated?

Sectional density is defined as the ratio of a projectile's mass to its cross-sectional area. This measurement is critical in understanding how the projectile behaves when it travels through a medium, such as air or water, as it can influence penetration and terminal ballistics.

To calculate sectional density, you take the mass of the projectile (usually measured in grains or grams) and divide it by the area of its cross-section, typically measured in square inches or square centimeters. The cross-sectional area is determined based on the shape of the projectile—typically a circle for cylindrical projectiles.

This ratio provides a numerical representation of how 'heavy' a projectile is for its size, impacting its ballistic performance. A projectile with a higher sectional density is generally more effective at penetrating targets compared to one with a lower sectional density, as it has more mass concentrated in a smaller area. The focus on density over just mass or merely the size of the projectile clarifies how these factors interplay when considering the effectiveness of the projectile in various conditions.