Is this info in The Parker Story? Thanks

We can even choose loads that reproduce the ballistics of the loads for which the guns were designed

DuPont Ballistic Table published in Parker Brothers' “The Small Bore Shotgun” c. 1920 http://parkerguns.org/pages/PDF%20Do...%20Shotgun.pdf
It is clear that this table converts Long Tons to PSI simply by multiplying by 2240; NOT using Burrard’s conversion
p. 7
“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…”
Original “E.C.” and “Schultze” were 14 grains/dram

http://pic20.picturetrail.com:80/VOL.../414020464.jpg

Numbers were measured by crushers and 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 (Modern SAAMI limit is 11,500 psi)
DENSE Smokeless Powder pressures would be 1000 - 1,500 psi higher

II kill just as many birds with 2 1/2 shells as I do with 2 3/4 shells and with less recoil.

Parker Service and Proof Load table published in the 1930s and reproduced in the "The Parker Story" p. 515. 12g 2 3/4" shell Service Pressure is 10,500 psi. Definitive proof is 15,900 psi or 7.10 Long Tons. The pressure was measured using LUP and modern transducer values would be about 10% higher.

http://pic20.picturetrail.com:80/VOL.../408978095.jpg

We’re getting off topic from OP but while we’re at it here’s some interesting proofing info from TPS

Thank you Ron. Those Lifter charges are of course for Black Powder and would have run about 1/2 of Bulk Smokeless introduced early 1890s.