I truly cannot understand why anyone would even think the bottom layer of the shot would not be the most deformed. That's the end the pressure hits it from. While he was doing that did he by any chance test for the difference in deformation of an equal shot load from various gauges. That I believe would be quite informative.
Also, I still agree with his statement which brought this on that as long as the pressure does not exceed what the gun was designed for one is not doing it any great favor by going to Extreme Low-Pressure loads.
I have been loading both Twist & Damascus to around 8K for 40 years or so now & have experienced no problems. Most of my guns had undoubtedly fired many "Proof" loads of off the shelf SAAMI spec loads & are all still going strong.
