[Unclenick]

It would be hard to get consistent thermometer readings, but the Tempilaq temperature indicator will work for you if you want an indicator.

I got your sizing and post-chamber dimensions twisted around in my mind between reading your OP and the more recent posts. I'd suggest you take your longest and shortest cases and shoot and neck size them only for several rounds; no body die. Measure after each firing and watch for each to stop growing the case headspace measurement and to start getting snug going into the chamber. You could plot a graph, and I'd bet you'll find they both converge on stopping at the same length. That growth stopping point should reflect the actual chamber size pretty closely.

Work the bolt slowly. Hatcher noted he could size a .30-06 something like six or nine thousandths (I forget which) just by working the 1917 bolt fast. Same for extraction on opening the bolt. Slow and gentle to keep from affecting the fired case size.