Clark,
Vernon Speer also didn't have any pressure data. He did buy a copper/lead crusher outfit, but apparently nobody at Speer could figure out how to use it and get consistent results (possibly because they used it in widely varying temperatures, not unknown in Lewiston, whether in winter or summer). So he used case-head expansion.
I have tested CHE in a piezo lab, and it did not work very consistently.
I started reloading ~1999, and within a year had worked up hundreds of loads to the point brass destruction or gun destruction in rifles and handguns. I had earlier made my money by designing power supplies and overloading them to destruction in an effort to find the weak spots in my design. My reloading kit came with "Speer 12" 1994, which I soon realized listed as max loads, loads that had wildly different safety margins. Within 2 years I had over 60 load books, mostly old ones from Ebay. The loads I worked up to brass failure in strong rifles and backed off a calculated safety margin had a kinship with the Sierra load books. My loads were not exactly their loads, but they were proportional. Sierra must at least be doing something based on reality to get consistent safety margins.
