We do seem to be posing many more questions than answers. I suppose the idea that 3 4 pellet strikes of sufficient energy will reliably break a target may have come from the fact that you rarely pick up an unbroken clay with evidence of more than 4 strikes. However you do pick up loads with evidence of 1 or 2 strike, particularly on trap disciplines. I did once pick up a clay with 7 strikes, but I guess someone was probably using 9s on an edge on distant target.
Just to add another not too scientific experiment to the melting pot. I had 3 very good shots at he ground a few years back and they took on a walk back challenge. They started on a high crossing target with 28g/9s and walked back. It was amazing that they got back to a point where you could hear the clay being hit without it breaking, yet 1 yard closer it broke consistently. They then changed to 7 shot which gave them another 5 yards or so and the same thing happened. The result of the contest was a break at 82 yards using a 36g/4 !!
The point of this observation is not the extreme range you can break a clay at but the narrow margin at which the energy of a pellet runs out. Now I cant tell you how many 9s were hitting the target when it stopped breaking but there was sufficient to hear it tinkle on the clay. The point I am trying to make is that if there is insufficient energy in the individual pellets to do damage it doesnt really matter how many hit the target it will not break.
John