Considering 1 1/4 ounce "normal" field loads here and 2 3/4" 1 1/2oz. oz. duck & goose loads, both lead of course, the 1 1/8oz. certainly sounds like a weak "heavy" load.
I was under the impression that 1 1/8oz was a "normal" 12 & 16 bore load and 1oz. was a "normal" 20 bore load.
These were "normal" for me in the 1960's, both 12 and 20bore.

The condition is lovely. A desirable gun, even if a week bit tight on the chokes.