Edge is 100% correct.
I used to think the powder burn rate chart was non variable and etched in stone. After talking to Hodgdon some time back, I learned this wasn't the case at all. Hodgdon told me the chart was just kind of a general guide and that a powders burn rate was not a constant and the burn rate could change every time a new variable was introduced. He said many powders are close, sometimes, even very close but to never think you can substitute one powder for another based on the burn rate chart.