Sectional density is the ratio of an object's weight to its cross-sectional area. It conveys the ability for an object to overcome resistance. When a projectile is in flight or impacting an object, it is the sectional density of that projectile which will determine how efficiently it can overcome the resistance to air or object. The greater the sectional density is for a projectile the greater its efficiency is and therefore ability to overcome the resistance of air and object.

Sectional density is stated as:

• SD = Sectional Density
• M = Mass of the object, kg or lb
• A = cross-sectional area, m² or in²

or

• d = diameter of the circle or the bullet's caliber

Units are kg/m² or lb/in².
In Europe the derivative unit g/cm² is also used in literature regarding small arms projectiles to get a number in front of the decimal separator.

Use in ballistics

The sectional density of a projectile can be employed in two area of ballistics. Within external ballistics, when the sectional density of a projectile is divided by its form factor it yields the projectile's ballistic coefficient.

Within terminal ballistics, the sectional density of a projectile determines penetration. If all other factors are equal, the projectile with the greatest amount of sectional density will penetrate the deepest.

External links

• The Sectional Density of Rifle Bullets By Chuck Hawks