Pressure/distance curve from "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe; E.I. du Pont de Nemours & Co., 1933.
Validated by Sherman Bell "Finding Out for Myself, Part VI, Smokeless vs Black", in The Double Gun Journal - Summer 2002, p.19
DuPont Oval was the first progressive burning powder developed for the 1922 introduction of Western Cartridge Company’s 12g 'Super-X Field' 2 3/4” 1 1/4 oz. 3 3/4 Dram Equiv. shell and the 3” 'Record' with 1 3/8 oz. of shot.
DuPont MX became PB, so neither of the smokeless powders are rapid burning.