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At the risk of repeating myself...I will because this is probably the most important summary to answer the question "What load should I use for my vintage gun (which has been evaluated by a double gun specialist smith and found to have adequate wall thickness and mechanical & stock integrity)?"

c. 1900: The �standard� U.S. 12 gauge field and inanimate target load was 1 1/4 oz. shot with 3 1/4 Dram Equivalent (1220 fps) of Bulk Smokeless with a modern transducer pressure of 8000 - 9500 psi.
Just before WWI: The �standard� U.S. 12g field and inanimate target load was 1 1/8 oz. shot with 3 Dr. Eq. (1200 fps) Dense Smokeless with a transducer pressure of 8,500 - 10,000 psi.

12g pressures
1 1/8 oz. 3 Drams (82 gr) Curtis & Harvey�s No. 4, T.S. Black Powder (somewhat similar to medium grain FFg) was about 6500 psi.
For comparison, 1 1/8 oz. 3 Drams (1200 fps) of DuPont FFFg Black Powder (82 grains) is about 5000 psi.

1 1/8 oz. 3 Dram Equivalent of BULK Smokeless was 6500 - 7500 psi.
1 1/8 oz. 3 Dr. Eq. of DENSE Smokeless was 8,500 - 10,000 psi.
1 1/8 oz. 3 1/4 Dr. Eq. BULK Smokeless was about 8500 psi.
1 1/8 oz. 3 1/4 Dr. Eq. DENSE Smokeless was 9500 - 10,500 psi.

1 1/4 oz. 3 1/2 Dr. Eq. BULK Smokeless was about 11,750 psi
1 1/4 oz. 3 1/2 Dr. Eq. DENSE Smokeless was 12,600 psi
Pressure is beyond the modern SAAMI recommendation of 11,500 psi

16g - 1 oz. 2 3/4 Dr. Eq. BULK Smokeless was about 7000 psi.

20g
7/8 oz. 2 1/2 Dr. Eq. BULK Smokeless was 8000-9000 psi.
7/8 oz. 2 1/2 Dr. Eq. DENSE Smokeless was about 11,000 psi.
Up until about WWI the standard 20g load in the U.S. was 7/8 oz. with 2 1/4 Dr. Eq. Bulk or Dense Smokeless powder.
7/8 oz. with 2 1/2 Dr. Eq. had been the standard British 20g load even before the 20g was offered by U.S. makers.

Thanks, Drew. Did you convert those old LUP readings to approximate psi as measured by modern transducers? If not, that would put those 1 1/4 oz loads well beyond the current SAAMI standard.

The reported pressures are converted to modern piezo transducer numbers using Burrard�s formula if originally expressed as Tons/sq. inch by LUP (Lead [Crusher] Units Pressure), or by adding 10-14% if expressed as PSI by LUP

Reported pressures varied significantly depending on pre-WWI British, between the wars U.S. (mostly Coxe's data), and post-WWII

Thanks. It gets very confusing when you read older stuff on pressure, even without the extra confusion the Brits caused when they started using the "tons" figures.

Indeed Larry. Even Wallace H. Coxe joined the "Tons" parade

"Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics", 1931

Western Cartridge Company�s 12g �Super-X Field� 2 3/4� 1 1/4 oz. 3 3/4 Dram Equiv. shell with DuPont Oval was introduced in 1922. Dram Eq. is listed as 3 but is much more likely 3 3/4.
Charge was 1 1/4 oz.

Using the estimated Tons Lead Crusher Pressure (Cp) conversion to PSI (pound force per square inch) (Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI.

Ballistite maximum pressure at 1� was 4.9 Long Tons = 15,344 psi
Schultze at 1 3/4� was 4.5 Long Tons = 14,000 psi
DuPont Bulk at 1 2/3� was 4.1 Long Tons = 12,656 psi
FFFg at 1 1/2� was 3.8 Long Tons = 11,648 psi
Oval at 2� was 3.5 Long Tons = 10,640 psi
All the curves essentially meet at about 3 1/2�.



Those are serious beyond SAAMI max. pressures in loads which the turn-of-the-century Live Pigeon shooters were using routinely, with those "time bomb" Damascus barrels