Originally Posted by Drew Hause
Fortunately we have numbers to prove that ed is incorrect.

DuPont Ballistic Table that was published in Parker Brothers' “The Small Bore Shotgun” c. 1920
http://parkerguns.org/pages/PDF%20Documents/Small%20Bore%20Shotgun.pdf
It is clear that this table converts Long Tons to PSI simply by multiplying by 2240; NOT using Burrard’s conversion
“All powders referred to on these pages are of the bulk nitro kind ranging from 12 (“New Schultze”, New “E.C. Improved No. 2”) to 13 1/3 (original DuPont Bulk) grains per dram…”
DuPont Bulk was introduced in 1893
"New Schultze" and "E.C. Improved" in 1903
Dense Smokeless powder pressures were higher. "Infallible" was introduced by Laflin & Rand in 1900

[Linked Image from photos.smugmug.com]

Numbers require adding 10 - 14% for modern piezo transducer pressures.
12 gauge
3 Dr. Eq. 1 1/8 oz. = 8,110 psi
3 1/4 Dr. Eq. 1 1/8 oz. = 8,960 psi
3 1/2 Dr. Eq. 1 1/4 oz. = 9,900 psi
16 gauge
2 3/4 Dr. Eq. 7/8 oz. = 7,035 psi
3 Dr. Eq. 1 oz. = 8,980 psi
20 gauge
2 1/2 Dr. Eq. 7/8 oz. = 12,655 psi

Very similar to modern pressures when adding 10-14%, and the 20g far exceeds the SAAMI recommended max. of 11,500 psi

If ed has post-WWI pressure data documenting higher pressures he is invited to post the information.