A very helpful pressure-distance graph dated June 10, 1929, from the McCracken Research Library, Buffalo Bill Center of the West (found by Gary Rennles) and used by permission
http://library.centerofthewest.org/cdm/singleitem/collection/WRAC/id/8149/rec/107

The digital image is part of the Winchester Repeating Arms Company Collection but includes a notation “Hunter Arms Co”. WRAC was acquired by Western Cartridge Co. Dec. 22, 1931, so it is impossible to know if the curve was generated by Winchester, Western, Hunter Arms, or (very possibly) the Burnside Laboratory of the E.I. du Pont de Nemours & Co.

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PROOF LOADS
Loaded with FFFg black powder. Shot presumed to be No. 6.
Pressures were measured by crushers (LUP - Lead Units Pressure) and modern piezoelectric transducer measurements would by 10 – 14% higher
F - 10g 2 7/8” 9.5 Drams with 2.36 oz. shot = 16,000 psi
A - 12g 3” 8.265 Drams with 2.187 oz. shot = 17,250 psi
G - 12g 2 3/4” 7.53 Drams with 2 oz. shot = pressure not recorded
B - 12g 2 3/4” 6.5 Drams with 1.687 oz. shot = 14,200 psi
C - 16g 2 9/16” 6.5 Drams with 1.687 oz. shot = 13,750 psi
It seems likely the ‘B’ 12g and ‘C’ 16g labels were switched
D - 20g 2 3/4” 5.74 Drams with 1.5 oz. shot = 14,625 psi
E - .410 2 1/2” 2.377 Drams with .624 oz. = 15,625 psi

MAXIMUM STANDARD LOADS
1” peak pressures
H - 12g 3” ‘Record’ 1 3/8 oz. shot presumed 1275 – 1295 fps = 13,250 psi
I - 12g 2 3/4” ‘Field’ 1 1/4 oz. shot presumed 1330 fps = 10,750 psi
The label ‘J’ for 28 gr. Ballistite and ‘K’ for 3 1/2 Drams DuPont Bulk appear to have been switched on the pressure curve graph. Dense Ballistite clearly generated greater pressure than DuPont Bulk.
K - 12g 2 3/4” 1 1/4 oz. 28 gr. Ballistite = 12,900 psi
J - 12g 2 3/4” 1 1/4 oz. 3 1/2 Drams DuPont Bulk = 10,000 psi

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The pressure curves essentially meet at 5” at 7000 psi; at 10.1” 2625 psi (DuPont Bulk) to 3000 psi; at 15.5” 2000 psi; at 22.1” 1500 psi

[Linked Image from photos.smugmug.com]

More vintage pressure-distance curves are at the bottom here
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/edit