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Ballistic Coefficient Calculator

Calculate ballistic coefficient (BC) from bullet weight, diameter, and drag model. Compare G1 and G7 BC for long-range shooting trajectory.

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Inputs that matter
Bullet Weight, Muzzle Velocity, Velocity at Distance, Distance, and 1 more
Output to expect
Ballistic Coefficient Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

BC Definition

BC = SD / i where SD is sectional density (weight/area) and i is form factor vs the standard projectile (G1 or G7 reference). Higher BC retains velocity better downrange.

BC = SD / form factor; SD = weight (lb) / diameter² (in)

G1 vs G7 Drag Models

G1 uses a flat-base reference — common in hunting ammo catalogs. G7 uses a boat-tail reference — more accurate for modern long-range bullets. G7 BC is typically 0.5–0.6 of G1 for same bullet.

BC_G7 ≈ BC_G1 × 0.55 (approximate conversion for boat-tails)

Form Factor from Geometry

Form factor derives from ogive radius, boat-tail angle, and meplat diameter relative to caliber. Long ogive and boat-tail reduce form factor, increasing BC.

i = form factor from bullet profile vs G7 standard

Updated: July 2026

Example Scenarios

Convert to G7: ~0.462 × 0.55 ≈ 0.254 G7 BC for Strelok or Applied Ballistics solver. Use G7 for trajectories beyond 600 yards.

105 gr .243 (SD 0.252) vs 175 gr .308 (SD 0.264). Similar SD but .308 boat-tail may have higher BC due to better form factor at same SD.

Chronograph at muzzle and 500 yards; solver back-calculates BC. Published BC may vary ±5% from your rifle's actual muzzle velocity and atmospheric conditions.

Common Mistakes to Avoid

Entering G1 BC into a G7-based ballistic solver

G1 and G7 are different drag models — using G1 BC in G7 software causes significant elevation errors past 600 yards. Convert or use matching model.

Assuming published BC applies at all velocities

BC drops through the transonic zone. Long-range solvers use velocity-dependent BC curves (multiple BC values) for accuracy past 800 yards.

FAQ

G7 BC above 0.250 is solid for 1000-yard work. Elite LR bullets exceed G7 0.320. Hunting bullets typically G7 0.150–0.220 — adequate to 400–600 yards.

Use G7 for boat-tail match bullets — more accurate beyond 600 yards. G1 works for flat-base hunting bullets at shorter range. Never mix G1 BC with G7 drag model.

Yes — BC varies with Mach number (transonic effects). Manufacturers publish average BC over a velocity range. Transonic zone (Mach 0.9–1.1) shows BC instability.

BC is a bullet property, but air density at altitude reduces drag. Trajectory solvers adjust for density altitude — BC value stays the same, drop decreases at high elevation.

Approximate BC from sectional density and estimated form factor. For precision, use manufacturer data or Doppler radar-derived BC from lab testing.

About Ballistic Coefficient Calculator

Ballistic coefficient (BC) measures a bullet's ability to overcome air resistance compared to a standard reference shape. This calculator estimates or converts BC from bullet dimensions, weight, and drag model for trajectory software.