Like Duckdog says, the measure is by weight for the mix. H42 is a mix that the US military came up with in the 1890's to get rid of the using glass, FWIW.
Something to keep in mind is that potassium perchlorate will be a bit more corrosive than potassium chlorate. The perchlorate will will form hydrochloric acid when fired. But it is safer in a factory environment. If someone tries it, please report back as to how it goes.
But my thinking is when it's easy to get exactly what a mix used(H48 and H42) that was carefully formulated and test to meet sensitivity, reliability, burn time, etc I like to stick with that. But I've got so many other thing in mind I can test, maybe I just kind figure good enough.
Glad to hear that I'm not the only one that is staying inside.