To clarify, pre-WWI English 1 1/2 oz. shells were black powder
1904-1914 W.J. Jeffrey & Co. catalogs (courtesy of Boyd Taylor Thompson) listed the Jeffery "Long Range" hammerless "Waterfowl" gun available in 3" chambers that "can be used with from 4-5 drams of black powder and 1 3/8 to 1 1/2 oz. of Shot".
The standard Pigeon load of 1 1/4 oz. 3 1/4 Drams Curtis & Harvey’s No. 4 T.S. (Black Powder) was about 8500 psi.
Live Bird loads with 1 1/4 oz. 3 1/2 Dr. Eq. Bulk
Smokeless Powder would be about 11,750 psi
The "Magnum" English 12bores were contemporary with the U.S. "Long Range" guns and Western's Super-X boomers
