Ballistics - Equations - Sectional Density

Sectional density equations and calculations. References and a list of variables are at the bottom of this page.

Sectional Density and Ballistic Coefficient

The BC, or ballistic coefficient is defined as:

where the diameter is specified in inches and the weight in pounds and the form factor is found using:

The sectional density is defined as:

making the ballistic coefficient

So this means that the ballistic coefficient is proportional to the weight of the bullet and inversely proportional to the diameter squared. (Keep in mind that the ballistic coefficient is also inversely proportional to the form factor which depends on the shape of the bullet!)

Calculation of the sectional density is straight forward. For a 300 grain, .338 caliber bullet, the sectional density is:

NOTE: With the common definition of the sectional density, the units have to be converted when used with drag functions, velocity, etc, to convert the in² to ft² resulting in a factor of 144.

Variables

References

Hatcher's Notebook, Julian S. Hatcher, Major General, USA, retired, Stackpole Books, Harrisburg, Pennsylvania, Second printing, 1966.

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