Sorry, but I have to disagree with Guffey on one point:
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The case head is measured first, loaded and fired and measured again, the difference is .001, the .001 should be expected every time that case is loaded if the same load is used...
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The case head typically does NOT expand the same amount with each firing of the same load. Typically, it will expand the FIRST time its compressive strength is exceeded. That expansion will work-harden the brass so that it will have a new, higher compressive strength. If subjected to the same or even slightly higher load again, it usually will not expand at all. Somewhat higher pressure is required to cause more expansion.
Richard Lee's book has a good discussion of this, with an example of how much overpresssure you could get by looking for some standard amount of head expansion in a case that has been fired a few times with increasing loads.
So, please don't think that you can grab any old case and see if the head expands more than 0.0003" to see whether your load is still safe enough as you keep adding more powder.
PRESSURE RING measurements are a different matter. There, fired diameter should be ABOUT the same for each firing of the case with the same load pressure. But, there is work-hardening happening there, too, and how you resize the cases affects what you can do with that technique, plus it tops-out at some pressure (depending somewhat on chamber characteristics).
BOTH techniques take considerable study and skill to avoid unsafe assumptions and practices. There is a lot of MIS-information floating around the Net and in some gun magazines on these two techniques. If you are going to use either, I STRONGLY suggest that you do some experimentation to see what happens with these measurements with YOUR gun when you use repeated firings with WELL KNOWN, PRESSURE-TESTED DATA of various pressures BEFORE you start relying on it for other loads.
SL1