When you collect velocity data, how many shots do you consider relevant?

[Doublehelix]

I know nothing about statistics, but I always worry about high ES numbers for when I need to make a specific Power Factor. I find that some powders seem to always produce higher ES numbers (Titegroup anybody?), but other powders (like WST and N320) seem to produce lower ES numbers consistently.

Some of this is variance in power drop consistency I am sure, but with powders like Titegroup, even a small change or variance in charge seems to have a significant affect on velocity variation.