Bill: if you could please post a full size close up of the barrels flats, several here could tell you the actually max. load and pressure for which the gun was reproved. Opinions are helpful,
numbers are moreso 
1925 - 1954 12g barrel flats were marked with chamber length and 1 1/8 or 1 1/4 oz.
In 1925, the 2 1/2” & 2 5/8” 12g max. service load was reduced to 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,682 psi by Burrard’s conversion.
The 2 3/4” 12g max. service load was 3 3/8 Dr. Eq. with 1 1/4 oz. shot with a mean pressure of 3 1/2 tons = 10,427 psi by Burrard’s conversion.
This would be even better
3 Dram 1 1/8 oz. shot
