Stan,
The burn rates are the key as you state. Kind of reminds me of the difference in sound of say the 3" on the tanker to the 5" on the destroyer to the 8" on the crusier to the 16" on the battle ship. They go from a sharp "crack" to the "pop" on the 5" to the "whoose" on the 8" to the "gentle whoose" of the 16". All have to do with the burn rate. I would think in the late unpleasandness the technology was not able to control the mix of the various powders. I think it was more of an art than a science. What say you?
FC