Us non-deep thinkin' types do better with pictures
Sherman Bell’s pressure testing published in
The Double Gun Journal Summer 2002 “Finding Out for Myself, Part VI, Smokeless vs Black”, p.19, and summarized in Volume 17: Issue 4, Winter 2006, p. 39
1 1/4 oz. 3 3/4 dram (102 gr.) GOEX FFFg Black Powder at 1240 fps and the equivalent load of Blue Dot. That is a boomer load few of us are likely to be using in a vintage double
................1 inch........6 inches.......12 inches
GOEX.........5900 psi......4100...........2100
Blue Dot.....6000..........4300...........2300
At 6" modern "non-progressive burning" powders are about 1/2 of Blue Dot's and GOEX pressures, and at 12" well below 2000 psi. Alliant data for 1 1/8 @ 1200fps
Alliant e3 - 17.2 grains = 10,950 peak psi
Red Dot - 18.3 gr = 10,300 psi
Green Dot - 21 gr = 8,900 psi
(Infallible) Unique - 22 grains = 8900 psi