Remember that all black powder and substitutes measure by VOLUME, not weight. A scoop of pyrodex is equal to a scoop of black powder is equal to a scoop of triple-7 is equal,,,etc. If you measure out 20 grains of black powder in a dipper, it will weigh (roughly) 20 grains weight. If you measure out 20 grains weight of Pyrodex, you will have an OVERLOAD. Use the volume measure. When the recipe calls for 20 grains, it means a 20 grain dipper, not 20 grains weight.
I think I emphasized that enough. Then again, maybe not. Call me if you have questions.