That's a "punt gun" back in the days when market hunting was legal they used to rig the front of a flat bottom boat with half a dozen of these 2 bore shotguns packed full of nails and tacks and nuts and whatever else they had on hand. Then before dawn they would row out to the middle of a river where the diving ducks would be all rafted up sleeping and wait for sunrise. When the ducks got up off the water they would pull a cord that was tied to the triggers of the guns and set em all off at once, dropping hundreds of ducks. Sometimes the plan would backfire though and the force of the guns going off would break up the wooden boats they were in droping them into the freezing water. Before they outlawed it, market hunting had almost wiped out North American waterfowl.