Originally Posted By: Researcher
From the 1890s into the early 1920s, these longer shot shells didn't carry a heavier payload than one could get in a 2 3/4 inch 12-gauge shell, just more/better wadding, which many serious Pigeon shooters believed to be an advantage.

Ah Ha!
That would explain why my British live pigeon 12g from the teens has a 3" chamber & 1 1/4 Oz shot proof.
It also explains why another British live pigeon 12g gun I have, that is 1925-26 manufacture is chambered 3" with 1 1/2 Oz shot weight proof.
O.M