"The powder Federal uses is non-cannister grade. Early Federal .470 varied considerably, lot to lot. I hear they're adjusting the charge now to allow for density variations between lots. 7.5% isn't surprising. I've run into that much with off the rack RL 15."

Do you mind explaing this in more detail? What is cannister grade and what is powder density variation? I'm not stupid, but these are new terms for me.