Now that it's February, everything is closed here in Iowa but rabbit season, which naturally brings up the subject of rabbit guns. Like the Most Interesting Man in the World, I don't shoot rabbits often, but I when I do, I shoot them with a shotgun.
Usually I shoot rabbits when I'm bird hunting and my dog isn't looking. So my "rabbit gun" is whatever I'm carrying for pheasants or quail. That usually means an IC/M 12 gauge and whatever lead or non-toxic load I'm shooting that day.
The perfect rabbit gun, though, doesn't have to be a 12. Although I've never mangled a rabbit with a 12, it doesn't take a lot of pellets to kill a cottontail. In fact, the best rabbit shoot I ever went on was a quail hunt in which the quail didn't show up and the rabbits did.
We shot rabbits until our gamebags got too heavy and we killed them all with Skeet-choked 20 gauge O/Us and 7 1/2s. A 16 or 20 is all the rabbit gun anyone needs. You could go smaller, although if I hunted with a .410, I'd confine my shots to close range and only shoot at sitting rabbits when I could make a head shot.
The perfect rabbit gun, like a good grouse gun, should be light enough to carry one handed as you fend off brush with the other hand. And it would be a gun that I wouldn't mind taking into the brush in the first place. Mine would have an IC choke, and I'd load it with 5 shot, if only to put fewer stray pellets in the meat.
Of course, the even more perfect rabbit gun would be a combination gun like the old Savage Model 24 with a 20 gauge barrel under a .22 LR barrel, just in case you do spot a rabbit sitting still at 50-60 yards.