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Calculate muzzle energy in ft-lbs from bullet weight and muzzle velocity. Compare cartridge power for hunting and ballistic performance.
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 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 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 standardUpdated: July 2026
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.
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.
BC drops through the transonic zone. Long-range solvers use velocity-dependent BC curves (multiple BC values) for accuracy past 800 yards.
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.