What is the formula used to calculate sectional density?

The formula for calculating sectional density is based on the relationship between the weight of a projectile and its cross-sectional area. Sectional density is an important factor in ballistics, as it helps determine how well a bullet will penetrate a target.

The correct calculation involves taking the weight of the projectile (often measured in grains for small arms ammunition) and dividing it by the square of its diameter (which is typically expressed in inches). This provides a measure of how much mass is concentrated in a given area, allowing for comparisons between different projectiles.

Using weight in grains and diameter squared allows for a consistent and useful metric in understanding the performance of different bullets. This relationship is critical in evaluating a bullet's effectiveness in terms of penetration and energy transfer on impact, which are vital considerations in both hunting and shooting sports.

The other options presented do not relate to the concept of sectional density accurately. They either pertain to different physical parameters or lack the necessary components to calculate sectional density.