I've used 410, 20ga and 12ga with good results. I'm partial to 410 for rabbits and 20 ga for doves. Grew up shooting rabbits with a 410 and considered it unsportsman-like to shoot them with anything heavier. Rabbits, (cottontails) are tender and easily torn up with heavy shells. And we shot for food as a kid, so protecting the edibility was paramount. Plus all I could afford was a single shot 410. I got really good at hitting running rabbits. I shoot doves with 20 and 12 ga. Last year, just for fun I took my newly acquired Remington 870 Wingmaster 12ga with 30" full choke and only took long shots with 7.5 field loads. Amazing how far that gun will shoot. But, I prefer my fully restored Remington Model 17 20ga with full choke.