Ballistic coefficient: how well your bullet fights drag

Every bullet sheds velocity to air resistance from the instant it leaves the muzzle. Ballistic coefficient scores how slowly that happens: a higher BC bullet keeps more speed, arrives sooner, drops less and gets pushed less by wind. It is a comparison to a standard reference projectile, not a physical property like weight.

Where the number comes from

Sectional density rewards heavy-for-calibre bullets; the form factor rewards sleek ones. A long, heavy, boat-tailed match bullet scores high on both, which is why it holds velocity so much better than a light flat-base of the same calibre.

G1 vs G7

A BC is always quoted against a drag model. G1 references a flat-based 19th-century projectile shape — still the industry default, and fine for flat-base and traditional hunting bullets. G7 references a modern boat-tail shape, so its numbers stay consistent across the velocity range of low-drag match bullets. G7 values are much smaller than G1 values for the same bullet; they are different scales, not different performance.

What BC changes downrange

BC works through retained velocity. Less drag means the bullet spends less time in flight, so gravity and wind get less time to act. Wind drift is where the difference is most dramatic — doubling BC roughly halves drift. Inside 100 yards the effect is negligible; past 500 it dominates.

Why BC changes with velocity

Drag behaviour shifts with speed, so BC is not truly constant — some makers publish stepped values per velocity band. The shift is most violent in the transonic region (roughly Mach 1.2 down to 0.8), where shockwaves reorganise and bullets can lose stability. For shooting inside 600 yards a single averaged BC is fine; near transonic range, stepped values and a G7 model earn their keep.