Unfortunately, breaking down the pressure curve per grain of each of the powders in the presence of the other would be both a long and dangerous task.
More long in the beginning, and much more dangerous towards the end....Don't think thats justifies the means...but hey- they aren't my fingers !
"A friend (chemical engineer) with experience in the pharmaceutical industry tells me it is notoriously difficult to uniformly blend two different dry powders. I have no reason to doubt that."
Nor do I, thats part of the difficulty. You would have to weigh out each individual round one at a time. You could not bulk mix them accurately.
Impossible... no. Anything is possible given time, equipment, and desire. Remember- helicopters don't fly on paper... Someone had to build one that worked to show all those crazy "forum-jockeys" of the past that he was right.
However
"It would be like introducing your two girlfriends to each other and taking them both on a date. The outcome could be amazing, but you are much, much more likely to end up with a black eye and a missing tooth! "
Probably sums up most of the max load end results quite nicely.
Lots of injuries in that helicopter path, too.