[Unclenick]

From load data, take the difference in the highest and lowest velocity for your cartridge with each powder and divide it by the number of grains difference in charge weight used to produce that difference in velocity. This gives you fps/grain in the normal load pressure range. Generally speaking, the smaller that number is, the less sensitivity the powder will have to things that affect pressure, be it charge weight error or temperature. It's not exact, but you can usually use it to tell a powder that will be more picky about conditions from one that will be less so.