The 20% variation is I believe industry/military standard for bulk powders which are shipped by the train load. The reality is that even for bulk powders manufacturers try to hold it to a reduced variation. When whoever orders the powder receives it it is standard practice to blend lots back to a more uniform standard. But you already know all this. You took it literally as R22 has a 20% lot to lot variation, what I meant is it starts off that way. When it leaves the Alliant factory it is blended and more uniform.
When it leaves the factory it can vary up to 20% but by the time it is blended and repackaged most of that variation is reduced. But I will hold to my statement that MRP is held to higher standards to begin with. I have seen lot to lot variations first hand with R22 and though I have used less MRP it has all been very uniform.
This may be intermojet lore but look at each and the grain size almost always varies more with R22 even if the color is the same. Maybe I should say same powder different standards. I think the different retardant idea came from 6mm Br.com a usually fairly reliable source. This makes me want to call Ranshot (the current NORMA distributer) again to see if I get the same answer, chances are I won't.
