Stan;
With all due respect that is not a true test of the burning rate of black vs smokeless when confined inside a gun barrel. One characteristic of black is it burns at essentially the same rate under "All" conditions, smokeless does not. Its ease of ignition & the ability to burn unconfined are the reasons for its restrictions in shipping, storage etc. Black is slower burning than powders such as Unique, PB etc & anything faster.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra