Dennis, if you are going to engage in a patterning project, I'd suggest you read Dr. Andrew Jones's book, "Sporting Shotgun Performance." It deals in considerable detail with a statistically valid method of pattern testing. It will lead you to a digital photo based computer analysis of patterns.
Note that there is a lot of variability from one pattern to the next with the same variables (barrel, choke, load). The book shows that ten (yes, 10) sample shots are required to define a pattern. I suspect that much of the variation in results found by previous researchers is because they shot too few samples.
I would dearly love to see some valid .410 pattern research. You seem to have a very good test bed with a control barrel and a candidate barrel, both with tight choke that can be opened slowly. If you are going to do the work, I'd suggest you do it really right.
DDA
Best
