PETER THEOBALD says: Fast crossing or overhead birds always seem to be killed more cleanly because they tend to get caught in the shot string of an accurately placed shot.
A slow approaching woody does not present much of a target, so invariably gets hit in the wings, which brings it down but does not kill it.
The solution is to either use more choke, or, as I do, deliberately turn the bird and shoot it as a crosser.
Got a question? Contact: firstname.lastname@example.org or Sporting Gun, PO Box 157, Stamford, Lincolnshire PE9 9FU