Too small, too prone to “spoilage”, and waaaayyyy harder to calculate existing stockpiles. It just wouldn’t be practical.
Mind you, that’s ignoring any of the should factor, and I am absolutely unwilling to engage in that debate
Edit: also, it’s too easy to improvise ammunition for simple firearms. You can’t really shove just anything into an autoloader and expect it to feed, but anyone with a machine shop could crank out something that would work, and the supplies just aren’t trackable the way something like ammonium nitrate is