Back in the day, I helped a friend, who is a meticulous reloader, with a project, by coming up with the print dimensions for a tight neck .300 Weatherby that had a freebore length that would allow bullets that were seated so that they would fit in the magazine of the Weatherby MK5 action, and touch the rifiling. Because there was no available load data, we approached load workup quite cautiously, starting in the lower loads of the reloading manual, and working up by half grains. I worked with a single case, neck sizing, firing and loading it at the range, with weighed charges. We used a permanent marker to mark the case across the head so that when we measured the belt diameter (with a .0001 mic.) that the measurement would be more uniform. The brass was Weatherby, which I believe was made by Norma. As we started, the first firing produces some belt expansion, even though the fired case gave no other indication of pressure. After that, until the last test, the belt diameter remained stable. As we got to higher and higher pressure, at some point, a circle appeared that showed that the pressure was high enough to move the brass slightly into the ejector hole. The diameter of that rifle's ejector was on the large side. finally, about a grain and a half over the manual maximum load, the belt diameter increased again, slightly, and we stopped. Generally, I do not find head expansion to be the indicator that I want to use for top pressure, because the brass from different manufacturers can be very different in hardness. I prefer to look at primers, bolt lift feel, and in some cases that bright spot that show up on case heads where the ejector hole is. Generally, over the years, I have become less prone to push the limits, having seen examples of what that can produce. Another thing that I keep track of is primer seating feel. If I start to feel primers seating easier, after only a few firings, I know that I need to retune at lower pressure.