Small steel and a crazy thick wad. Open chokes, let the shell be your choke control.
I shoot many rails, and obviously they aren't all that strong flying. Snipe I take on the flush typically. So the shots are usually within skeetish range.
Not a great answer, but economical. I'd prefer fiber wads, as the MM 2 3/4 wads are very heavy and don't break down via sunlight for years.
In a Twist or Damascus gun? I'm all set up for roll crimping with fiber wads and paper shells. Could I make this work with #7 steel? Is zinc-plated steel better? How about buffering with sawdust or cornmeal?