Dave is of course correct.
Field & Stream, 1912, “The Trap Gun and Some Loads” by E.C. Crossman
September, Part 1
https://books.google.com/books?id=OH...J&pg=PA537&lpg
October, Part 2 “Patterns and Loads”
https://books.google.com/books?id=dH...J&pg=PA628&lpg
Crossman listed the standard Trap load as 1 1/4 oz. 3 1/8 Dr. Eq.
In 1913 the Interstate Association submitted a poll to trapshooters:
Are you in favor of restricting loads for target shooting to 3 Drams Bulk, or the equivalent in Dense powder, and 1 1/8 oz. of shot?
Frank Butler – “Let me say that the shooter can break targets with a three dram one and one-eighth load if he holds right. Harold Money, who traveled as a professional for years, always used three Drams “Schultze” Powder and one and one-eighth shot.”
DuPont began an advertising campaign promoting 3 Dram loads in 1914
Forest & Stream
https://books.google.com/books?id=kB4cAQAAMAAJ&pg=PA835
https://books.google.com/books?id=kB4cAQAAMAAJ&pg=PA867
In 1919 the Executive Committee of the American Trapshooting Association voted on whether to establish the standard load a 1 1/8 oz. 3 Dr. Eq.
The proposal failed.
Arms and The Man, August 2, 1919
https://books.google.com/books?id=TB...C&pg=PA377&lpg
Bill: The Western Super-X Super-Ten shell with 1 5/8 ounces of shot with 4 3/4 Dr. Eq. of Progressive Burning Smokeless Powder in a 2 7/8" case was introduced about 1926. The Western Super-X Magnum-Ten with 2 ounces of shot and 5 Dr. Eq. of Progressive Burning Smokeless Powder in a 3 1/2" case was introduced in 1932.