Sectional Density (SD)
Definition
The ratio of a bullet's mass to the square of its diameter. Higher SD values predict greater penetration depth in a given medium because the projectile presents less frontal area per unit of driving mass. Used in penetration models by DSTL, FBI Ballistic Research Facility, and Indian CFSL.
- Formula
- Bullet mass divided by diameter squared
- Predicts
- Relative penetration depth in a given medium
- Used by
- DSTL, FBI Ballistic Research Facility, Indian CFSL
Common questions
Why does a higher sectional density improve penetration?+
It means less frontal area is carried per unit of driving mass, so the bullet loses velocity more slowly as it pushes through tissue or another medium, letting it travel further before it is stopped.
Is sectional density the only factor in a penetration model?+
No, it is combined with impact velocity, bullet construction and expansion behaviour, since a bullet that deforms or fragments on impact changes its effective frontal area partway through the penetration event.
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