Chuck,
I have no problem with either strain gauge or piezo transducer measurements to obtain pressure. I just know that if calibration to a repeatable standard isn't registered in the setup the data is no longer valid except to say this load is higher pressure than that load also measured on the same devices. The industry standard pressure guns are held to a specific set of internal dimensions and are regularly recalibrated to maintain accuracy of the output. I started dealing with both of these devices (before computers were available so the data was recorded by oscillascopes and Fastex cameras) in 1961 in connection with engineering military ordnance. When you ask an ammo company for data they are not able to relate it to your specific firearm. They can only tell you what pressure it should produce within certain statistically defined parameters in a gun of proper construction. The max avg of the lot tested in 12ga should be less than 11,500 psi, max probably lot mean 12,100psi and max probable sample mean 13,000psi. If the lot exceeds any of these values it is junk. Now we come to hobbists measuring a couple rounds from a lot and making pronouncements - doesn't cut it because the numbers tested are statistically insufficient on devices insufficiently demonstrated to be accurately calibrated. Fun hobby for sure and I have played with it myself on a friends equipment.
