Any 12 ga. drilling I've handled is a club. 2 1/2 in., 16 bore ammo is available from RST and others. They're also very easy to make and load on your own which is how a lot of us do it. As with oskar I've never felt handicapped by using 2 1/2 in. hulls.
There's lots of 8 X 57R, 7 X 57R and a host of other cartridges well past the century mark that are available in old drillings. A lot of them are either available over the counter or easily made with little investment or effort. My Jaeger in 9 X 57R comes to mind. One pass of 8 X 57R brass through a 9 X 57 die and I'm done.
A lot of the old drillings are going to require a little tinkering with the ammo but it's time and money well spent and, the results are usually more than satisfactory.
