Remember that in a formal driven shoot, and, especially, in one of the really high bird shoots, there will be a couple of lines of pickers-up in back of the guns. The last line may be several hunderd yards back, depending on the topography. Birds hit are marked and very few don't get picked up. After all, they are a cash crop for the landowner, who sells them twice, once to the guns and once to the gamedealers (for about 2% of the price to the guns!)