Found this while doing some searching for info on cast bullets, useful for those of us who don't have a chronograph:

Muzzle Velocity = 2518.4*X to the 0.344 power, where X=grains of powder/bullet wt. in grains

This was generated using 777 2f powder.

I checked it against the published velocities on the Hodgdon website for a variety of bullets and 90gr. of 777, and found it to be within +/- 30 fps. I would think that for most of us that use volumetric powder measures, that is more than accurate enough for calculating ball park ballistics. Pretty cool!