gallatin:
There will probably be some vocal disagreement with this, but in the absence of a full engineering lab, just go with the most steel. Look for a heavy-weight gun with a long deep action-bar, robust wide lumps, big diameter hinge-pin, thick chamber-walls, and plenty of meat everywhere you look. Stay away from light-weight, slim doubles with narrow or short lumps. You want a fowler or heavy pigeon gun, not a game gun. A third bite is mandatory IMHO, but many successful DRs don't have one I know.

No guarantees of course, but this should put you in the ball-park.