The gun was made for the progressive burning smokeless powder, high velocity, 12-gauge 3-inch shell with 1 3/8-ounce of shot --

[Linked Image from i.imgur.com]


[Linked Image from i.imgur.com]

The 1 5/8-ounce, 12-gauge, 3-inch magnum load came out in 1935 along with the Winchester Model 12 Heavy Duck.