The Potassium Chlorate I used, not Potassium Nitrate, was used as the oxygen producer in the detonating compound of the priming mixture.
5:1:1 was the ratio, or P.C. to Charcoal and Sulfur.
I used ground up charcoal Briquets and sublimed sulfur.
I was told by a chemist that my mix used VERY highly refined sulfur and he said: "who knows what chemicals you added with the briquets?"
A piece the size of a green pea on the bench-vice anvil, if a hammer was held in one hand and smacked onto the compound, would fling the hammer back over your shoulder.
Had some good snap to it.
Potassium Perchlorate is used in the making of Pyrodex. It is 17% of the mixture and that what makes it VERY corrosive.
I was informed that Perchlorate is different than Chlorate as it has 3 extra oxygen molecules in it's chemical makeup. I didn't 'take' chemistry in school.

You are right though, it is silly to regulate the chemicals, but not the product itself.
Of course, diesel fuel and nitrate fertilizer are both easily acquired.