Custom drag functions

Using your bullet's own drag coefficient versus Mach directly — how to import one, and why provenance is required.

G1 and G7 are reference projectile shapes; your BC scales your bullet onto one of them. A custom drag function skips the reference entirely: it is your bullet’s own drag coefficient versus Mach number, used directly — no BC involved.

Importing a curve

Import one as a CSV of mach,cd pairs (headers and junk lines are skipped; European semicolon/comma files work). The requirements:

At least two points.
Mach strictly increasing.
Cd positive.

Anything else is rejected with the reason.

Provenance is required

Provenance is required, on purpose. A drag curve is only as trustworthy as where it came from:

Manufacturer doppler-radar data (some publish it).
A digitized chart.
Your own truing.

“Some app had it” is not provenance.

When a curve is present

When a curve is present the BC field is ignored and the calculator says so. The drag scale (shown read-only) is the truing correction factor for that curve — replacing the curve resets it, because a correction trued against one curve is meaningless applied to another.