Interesting discussion, but I do feel that the wording "if the gun goes off" does leave a teeny bit of room for interpretation and I can understand why some (many?) would have thought this meant hearing the 'bang' noise.
My interpretation would be in accord with the man who paints his letters green, along lines of ...... if you're on target, fully prepared to take the shot, only to find that pulling the trigger results in the discovery of a failure to load pellet/close action/whatever then the firing cycle is complete and the result scored on the outcome of that cycle. Otherwise we'll have Styer owners modifying their guns to mute the 'click'
Perhaps we do need a ruling from Sparky or other UKAHFT senior.
Biggles