How to avoid case head separations . . . . . .
The pictures in post #1 show normal case expansion at the transition to the web (solid part of the case). Post # 11 shows the first signs of typical case head separation. As also shown, you can measure case thinning with the RCBS CaseMaster.
However, if you want to completely avoid case head separations, you'll need to set your die height accurately (not by guesswork). Take a look at the Digital Headspace Gauge, and you'll see how to adjust your die height perfectly. The Digital Headspace Gauge works on ALL different calibers, it's easy to use, and doesn't require any expensive bushings.