I beleive the term "shot string" refers to holes in a sheet of paper that are shot with a gun not moving and the piece of paper that is moving aproximately perpenducular to the shot. That is the target is struck by the first pellets and the following pellets string out across the paper illustrating the string. Using a game bird the string is not going to be illustrated it is just going to go behind the bird. If a slow motion camera is used rather than a moving target board the "string" would show as a swarm of pellets some leading others following. The later is the more accurate illustration of a shot string.