Stan;
Yes the Slower & faster in my statement is as appl;ied in the shotshell. As can be seen in the charts Drew posted DuPont Oval was the only one which had a slower pressure rise than black. The rest were all faster reached a higher peak & then fell off quicker. As DuPont Oval, or other progressive shotshell powders were not available for about the first 2˝ decades of smokeless powder use it becomes obvious those early bursts were not brought on by the cause to which they were attributed at the time.
Black Powder has the unique attribute of burning at essentially the same rate regardless of other factors,so yes it will burn unconfined while smokeless can be hard to ignite that way. The more heat & pressure is applied to smokeless the faster it burns.This is actually the attribute which allowed it to act in such a manner as to cause those bursts through delayed burning, a type of a "Semi-Hangfire" if you will.


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