Chronograph data

[dontgetcrabs]

Ballistics Coefficient is a product of velocity

BC is a product of mass, diameter , surface area and surface condition.

Why does BC go down as velocity slows?

[Bob33]

Ballistic coefficients do change slightly as velocity changes.

[Feanix]

Ballistics Coefficient is a product of velocity

BC is a product of mass, diameter , surface area and surface condition.

Surface area and surface condition do not equate to drag coefficient. Drag coefficient is a product of velocity. Most bullet manufacturers use standardized drag models when calculating their stated BC and most are averages. I think only Sierra lists different BC's for different velocities, and not on all bullets.

Getting off track.
Crunchy: I use chrono data as a check for consistency in my loads (ES AND SD) and use the average velocity as a starting point for trajectory. A standard deviation of 50 is pretty high. Make sure you charges and seating depth (measured from the ogive) are consistent. When i was tuning the load for my 308 i kept getting fairly large SD's and ended up changing primers.

[argie1891]

chronograph data is at the very least a heck of a lot easier to get than doing the complex math you are talking about.. now some of us have a high school education and are not well versed past addition and subtraction with a calculator. for my money I will buy the chrono and you guys with sharp pencils can figure it out your way. and please do me a favor and don't come back with how simple it is to figure as an old man like me would never spend the time or energy to figure out what you are talking about. argie1891