Ballistic Coefficient Calculator
Calculate ballistic coefficient from bullet mass, diameter, and form factor for trajectory and drag analysis.
What Is Ballistic Coefficient?
Ballistic coefficient (BC) describes how well a projectile resists air drag compared to a standard reference shape. Higher BC means less drop and drift over distance. Hunters and long-range shooters use BC with muzzle velocity to predict trajectory.
BC Formula
$$BC = \frac{m}{i \cdot d^2}$$\(m\) is mass in pounds, \(d\) is diameter in inches, and \(i\) is the form factor (shape drag relative to the reference). A .308 Winchester bullet weighing 168 grains with 0.308 in diameter and form factor 1 gives BC \(\approx 0.253\).
Units and Conversions
Ballistic tables in the United States typically use grains and inches. Convert grams to pounds by dividing by 453.592, and millimeters to inches by dividing by 25.4 before applying the formula.
Related tools: KD Calculator and Carat Weight Calculator.
Frequently Asked Questions
What is the form factor?
It compares the bullet's drag to a standard reference projectile. A sleek boat-tail bullet may have \(i < 1\); a blunt shape has a higher form factor and lower BC.
Does higher BC always mean better accuracy?
BC affects trajectory, not inherent accuracy. A high-BC bullet drifts less in wind and drops less, but barrel quality and load consistency still dominate precision.
Why use pounds and inches?
G1 and G7 drag models and published BC values in the shooting industry traditionally use imperial units for mass and caliber.
How does diameter affect BC?
BC is inversely proportional to diameter squared. A wider bullet of the same mass has a lower BC because it presents more frontal area to the air.
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