Ballistic Coefficient Calculator

Ballistic coefficient measures how well a projectile overcomes air drag.

How the Math Works

The ballistic coefficient (BC) quantifies how well a projectile resists air resistance during flight. It is calculated using the formula BC = SD / i, where SD (sectional density) represents the projectile's mass relative to its cross-sectional area, computed as (weight/7000) divided by diameter squared (in inches). The i factor accounts for the bullet's shape, typically ranging from 0.2 for flat-nosed bullets to 0.5 for pointed ones. A higher BC indicates superior wind penetration and retained velocity, making it critical for long-range shooting precision.

Practical Applications

To use this calculator, enter the projectile's weight in grains and diameter in inches, then select or input the appropriate shape factor (i) based on bullet design. For common hunting or target bullets, manufacturers often provide the i value in reloading manuals. Simply divide the calculated SD by the shape factor to determine BC. This value directly informs trajectory predictions in ballistics software, enabling shooters to select optimal ammunition for specific ranges and conditions without complex computations.

Day-to-Day Use

Understanding your projectile's ballistic coefficient helps you make smarter shooting choices in everyday scenarios like hunting or sport shooting. When selecting ammunition for deer hunting at medium distances, a higher BC bullet ensures flatter trajectory and less wind drift, increasing your effective range and hit probability. Similarly, competitive shooters use BC to match their load to course conditions, reducing sight adjustments needed. Even if you don't calculate it yourself, recognizing how BC affects performance guides informed decisions at gun shops or reloading supply stores, ensuring you choose the right bullet for your intended use.

Worked example

150 gr, .308", form factor 0.5 → SD 0.226, BC 0.452.

FAQ