Hi, John. Assuming you are primarily agreeing on the single pellet target breakage, consider the following. Are you aware of any other research on target breakage other than collecting unbroken targets and assessing hits? I'm not. Far as I know, Jones's work is unique for scientific determination of what is required to break targets.
As Jones notes in the book, there are many factors involved in the dynamics of whether the target breaks of not. There are zones of the target that are robust to a pellet strike, others that the pellet can penetrate with full expenditure of it energy, and still others that the pellet can penetrate without expenditure of full energy. Further, the angle at which the pellet strikes is important to the amount of energy imparted to the clay; penetration vs glancing.
When the clay is struck by a pellet imparting sufficient energy, a fracture initiates at the point of impact and spreads across the clay. Clays are actually very strong, but brittle. The spin of the target is exactly the force that tends to grow the fracture. The extreme example of this is the target that more of less falls in half in a clearly discernible time lag after the shot.
We have all seen targets emit a puff of dust and proceed merrily on their ways. Likewise, we have seen targets shed the proverbial visible chip, break in half or three pieces. These are more likely to be single pellet events than multi-pellet events. Only more likely, not exclusively.
The foregoing may not seem useful to the shooter. However, I'll give an example of how it has affected me. I no longer say such lines as, "You must have been behind that one since the chip came off the back edge." I now know that I have no idea how much rotation the target had between impact and fracture growth to chip shed. If the target had half a rotation, I would be 100% wrong.
Jones did not totally solve all shotgun pattern questions, but he did give us a wonderful set of data to build upon.
I have two suggestions: #1. read the book, and #2. don't bother shooting patterns unless you are going to do Jones's analysis.
I hope no one is offended. This is meant only as discussion.
DDA
