CaliberAtlas › Guides › Ballistic Coefficient Explained: G1, G7, and What BC Really Means
Ballistic coefficient is one of the most quoted — and most misunderstood — numbers on a box of ammunition. Here's what it actually measures and how to use it.
By Preston Willis · Published June 30, 2026 · Last updated July 18, 2026
Ballistic coefficient (BC) is a single number that describes how well a bullet overcomes air resistance in flight. A higher BC means the bullet is more aerodynamic: it sheds velocity more slowly, drops less at distance, drifts less in wind, and arrives with more retained energy. Two bullets can leave the muzzle at the same speed, but the one with the higher BC will be flatter-shooting and more wind-resistant downrange.
Technically, BC is the ratio of a bullet's sectional density to its form factor — a measure of how its shape compares to a standard reference projectile. You don't need the math to use it; you just need to know that BC bundles together a bullet's weight, diameter, and shape into one comparative figure.
BC is always measured relative to a standard projectile shape, and the two you'll see are G1 and G7. G1 is based on a flat-based, blunt-nosed reference bullet. It's the historical standard and the number most manufacturers print. G1 BC values are higher-looking, but they change with velocity, so a single G1 number is least accurate at long range.
G7 is based on a long, boat-tailed, spitzer reference bullet — a much closer match to modern low-drag match and hunting bullets. For those bullets, a G7 BC is more consistent across velocities and gives better long-range predictions.
The practical rule: for modern streamlined rifle bullets, prefer the G7 figure if it's published. For traditional flat-base or round-nose bullets, the G1 figure is appropriate. You cannot directly compare a G1 number to a G7 number or safely convert between them with a fixed multiplier; use the measured or manufacturer-published value for the matching drag model.
Imagine two .308-caliber bullets both launched at 2,700 fps — one with a G1 BC of 0.40 and one at 0.55. By 500 yards, the higher-BC bullet is traveling faster, has dropped noticeably less, and has drifted several inches less in a 10 mph crosswind. The difference compounds with distance, which is why long-range shooters obsess over BC while a 100-yard plinker can largely ignore it.
BC is most valuable as a comparison tool. When two loads are otherwise similar, the higher BC will be the better long-range performer. But BC never acts alone: muzzle velocity, bullet weight, and your zero all shape the final trajectory.
Match the metric to the job:
CaliberAtlas supports G1 and G7 in its calculator when the matching published BC is available. Stored per-cartridge reference tables remain G1-computed, while calculator results identify the drag model actually used. Try comparing two loadings of the same cartridge in the ballistic calculator to watch BC change the downrange numbers.