Just enjoying some pre-Thanksgiving pumpkin pie. Hope all of you are having an equally enjoyable evening.
Two comments:
MD is correct in recalling my test of pressure vs. flatness. A few years ago, I had a fit of ambition and started an article on evaluating pressure by looking at primers. So I loaded a couple of dozen cartridges ranging from mild to maximum, and touched them all off. Then I extracted the primers, marked them, and put them under a bench microscope. I arranged them from roundest to flatest, and found no correlation between powder charge and position in the arrangement. That article never saw the light of day. Bummer.
Again a few years ago Ken Oehler instrumented a pressure barrel with two piezo transducers, each feeding identical electronic channels. He also instrumented the same barrel with two strain gauge channels. Then he fired a series of shots ranging from pea shooter to bazooka. Given that data set, it was not a great task to derive the fundamental precision of both systems, as well as their accuracy. It turns out that each is as good as the other. Neither has a theoretical advantage. Which you use is simply a matter of convenience. The strain gauge system has the advantage of not requiring a hole in your chamber, and the physical quantity conversion chain is a little shorter than that of the piezo system.
Many people get hung up on the notion that they can't very well check the strain gauge against a known standard artifact. That's really not the problem they think it is. We know the rest mass of an electron to great precision, yet no one has ever built a suitable scale and wrestled a single electron into the weighing pan. We know the distances to the stars, but no one has ever laid a ruler along the path to one. There is no standard velocity artifact you can use to calibrate your chronograph. (Rumor has it that NIST did have some at one time, but someone peeked into the containers, and the standards all disappeared into the bush at highly accurate velocity.) There are no standard weight artifacts. What we think of as weight standards are really mass standards. Many of the measurements we confidently deal with on a day to day basis have no directly comparable calibration artifact, and we still get along just fine.
Last edited by denton; 11/24/20.
