G1 vs G7 drag models

Drag on a bullet changes with speed, and it does not change the same way for every bullet shape. A drag model is a reference projectile with a measured drag curve. A ballistic coefficient says how your bullet compares to that reference: 0.500 G1 means your bullet sheds speed like a G1 standard projectile with a sectional density ratio of 0.500.

G1 is a short, flat-base reference. G7 is a long boat-tail with a secant ogive. A modern match bullet looks far more like G7 than G1, which is why G7 coefficients hold steady across the speed range while G1 coefficients for the same bullet drift as velocity falls.

Use whatever your bullet maker published, and set the drag model to match. If both are published, prefer G7 for a long-range boat-tail and G1 for flat-base, round-nose and most hunting bullets. Never type a G7 number while the selector says G1 — you will be told your bullet drops roughly twice as much as it really does.

The solver carries the full drag-coefficient table for each standard family — G1, G2, G5, G6, G7 and G8 — as measured against the reference projectiles. At every integration step it looks up the drag coefficient for the bullet’s current Mach number on the table your coefficient was published against, then applies drag from real air density. Nothing is converted between families: a G7 number runs on the G7 curve.

This matters most where the two curves disagree, which is exactly where the old multiplier approach failed: the transonic region. A G7 bullet holds a nearly flat drag coefficient out to about Mach 0.9 and then spikes, while G1 climbs earlier and more gently. Solved properly, a long boat-tail keeps more velocity past 800 yards than a G1-equivalent estimate suggests.

Two honest limits remain. The coefficient itself is treated as a single value rather than as a velocity-banded set, and drift uses a lag-time crosswind model rather than a full six-degree-of- freedom solve. Transonic rows are still dimmed in the table, because bullet stability — not drag bookkeeping — is what makes that band unpredictable.

Put the same bullet in twice on the trajectory workspace, once as G1 and once as G7, and watch how the two lines separate past 600 yards.