Several black and smokeless pressure curves can be found in the links.
12g Black Powder peak pressures are only slightly lower than many modern smokeless loads
1 1/8 oz. 3 Drams (1200 fps) of DuPont FFFg (82 grains) is about 5000 psi.
1 1/8 oz. 3 Drams Curtis & Harvey’s No. 4 T.S. (82 grains; somewhat similar but not equivalent to medium grain FFg) was about 6500 psi.
1 1/4 oz. 3 1/4 Drams Curtis & Harvey’s No. 4 T.S. was about 8500 psi.
Black Powder substitute pressures from the 2001 “Lyman Black Powder Handbook & Loading Manual”
1 1/8 oz. with 100 gr. GOEX FFg at 1200 fps = 4,800 psi
1 1/8 oz. with 100 gr. Pyrodex RS at 1200 fps = 5,600 psi
