The 1913 Lefever Arms Co. catalog gives recommended loads in 12g going up to 3 1/2 Drams Black or Equivalent of Bulk or Dense Smokeless powders with 1 1/4 oz. shot, or 28 grains of Laflin & Rand Dense Infallible.
Comparative Loads from the Lefever Arms Co. in
The Outdoorsman's Handbook, 1920
http://books.google.com/books?id=Lr1DAQAAMAAJ&pg=PA138&lpgThe standard pre-WWI U.S. 12g Field and Target load was 1 1/8 oz. shot with 3 Dr. Eq. (1200 fps)
Dense (Ballistite or Infallible) Smokeless in a 2 3/4 case with a transducer pressure of 8,500 - 10,000 psi.
The 1 1/4 oz. with 3 1/4 Dram Equivalent (1220 fps) of
Bulk (DuPont, E.C., Schultze) Smokeless in a 2 5/8 or 2 3/4 case was still popular, with a modern transducer pressure of 8000 - 9500 psi.
