BC Truing from Chronograph
Back-solve a truer ballistic coefficient from a measured velocity at distance.
How this works
Manufacturer-published ballistic coefficients are measured under specific test conditions and don't always match how a particular rifle and load perform in the real world. "Truing" solves the problem in reverse: instead of trusting the catalog BC, it finds whichever BC value makes the trajectory model agree with a velocity you actually measured downrange.
One truing shot goes a long way
Because the model already knows your muzzle velocity, weight, and atmospheric conditions, a single well-measured velocity at a known distance is usually enough to true the BC for that load. This trued value is specific to your rifle, load, and roughly the conditions you tested in — retest occasionally, especially after a barrel change or a big shift in altitude or temperature.
Frequently asked questions
How many shots do I need to true my BC?
Often just one well-measured velocity at a known distance is enough, since the model already knows your muzzle velocity and other inputs — but a couple of confirming shots at different distances adds confidence.
Does trued BC apply to a different rifle with the same ammunition?
Not reliably — the trued value reflects your specific rifle's barrel and the conditions you tested in, not just the ammunition. A different rifle, even with identical ammunition, can shoot to a slightly different real-world BC.
Why not just trust the box's published BC?
Published BCs are measured under specific lab conditions and can run optimistic compared to what a specific rifle actually delivers — truing from your own chronograph data corrects for that gap.
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