Peak or Max pressure does not determine the velocity of a load. If for instance you load Red Dot & Unique both to give 1 1/8oz of shot 1200fps (3 DE) velocity your peak pressure will not be the same. The "Work" performed will be the same but it will be applied over a different "Curve". There is much more involved than just peak pressure. One large difference between BP & smokeless is their burning characteristics. BP burns at essentially the same rate regardless of external characteristics. This is not true of smokeless. While certainly common sense & caution need to be used, one is simply not going to run into problems as quick from an overload with black, nor are failures as apt to occur from "Underloads" as with smokeless. Except for the fouling BP is a handloaders dream.
Propellant type BP's burning rate is determined only by its granulation size. Smokeless burn rate is controlled by grain size, shape, configuration, as well as deterrant coatings etc & is made in a far wider range than is BP. In rifles BP is considered a "Fast" powder, in shotguns a compartively "Slow" powder. Many smokeless powders loaded to give comparative max pressure to black simply will not burn dependably under all temperture conditions. They are designed for specific purposes & trouble often lurks for those who try to use them outside their design.
