Some time ago I ran a rough pressure test on a custom .300 Weatherby chamber that had a short enough throat that you could touch the rifling with a loaded round that would fit in the magazine. We loaded at the range, and did the test with a single case. To see what head expansion was doing we used a 1" mike that would read to .0001" and measured the belt diameter, having first made an indexing mark across the head. The brass was Weatherby, which I believe is made by Norma. The first shot, which was well down in the book, showed movement, after that we did not see any until we were well over the book max. Before we got to that we saw an ejector smear on the case head. After we finished the test, we recorded the temperature and noted what we thought would be a safe maximum for future hunting loads.
If I was going to do this sort of test again, I think that I would use a group of once fired cases, and only use each case one time. For a rimless case, as an earlier post mentioned, a blade mic. would be a good way to read changes in the diameter of the bottom of the extractor groove.
A couple more things.... I don't think that AE cases show primer flattening at a given pressure to the same degree as more conventional case designs, and if you have a good fitting .062 firing pin tip, you will not get much of a crater. On the other hand, initial bolt lift issues can happen with any case design, if pressures are too high. Also, by loading at the range, using the same case for a pressure series, and priming with a hand tool, you will immediately feel any change in primer seating force. If your primers fall in too easily, your load is probably too hot.
