Most of what i have to say has been said, saving me lots of typing.
1) Primer appearance means very little. There is great variance in the hardness of individual primer cups. I just ran some 30 year-old WLR in some 30-06 loads that came out flat as a pancake, but the chronograph indicated relatively benign pressure. Primer cratering is more often the result of slop between the firing pin and the hole it slides through than high pressure. I have a (way) sub-MOA Christensen Mesa that always craters reasonable loads, regardless of pressure. Same for a pair of Rem M7 Predators in .243 and .223. The FN Mauser that flattened those old WLRs like a pancake had a perfectly fitted firing pin and absolutely zero cratering.
2) Sticky bolt lift, maybe accompanied by ejector marks, is usually a reliable indication of excess pressure. and in these "usually" situations you are likely pushing 70K PSI. But there are other things, like burrs around the ejector slot or plunger hole, or a rough chamber, that might sometimes show those signs at lesser pressures.
3) While case head expansion is worthless to determine absolute pressure, I have found it to be a very useful indication of relative pressure within a single lot of brass. And it's a good predictor of how long your brass is going to last. Less than .0005" CHE on virgin brass is a pretty good indicator of long brass life. And it should go without saying that you don't do CHE with a caliper. You need a micrometer, preferably a blade mic so you don't have to file case rims on unbelted or non-rebated cases, and the ability to use it to read measurements to .0001"
4) Best for Last - The Chrono is your friend. For a given load (and yes, there are other factors) speed is approximately equal to pressure. If the book max got 2975 FPS with powder x and bullet y, if you load your rifle (with the same length barrel!) to the same speed with powder x and bullet y, it might take one or two grains more or less than the book lists. But if you stop there, you are very likely in a safe place. And for that matter, different lots of the same powder could require the same consideration. If your extra-special custom load beats the book by 100 FPS, you are pretty reliably well over SAAMI max.
5) Which might not matter - There is nothing about necking down the 30-06 case (60K PSI max) by .031 to .277 that magically makes 65K PSI safe in your rifle. 65K is either safe or it's not in a particular action and that's why the .270 Win is a really bad candidate to hot-rod, while the 30-06 has a fair bit of "head room". But if either of them shows hard bolt lift or ejector marks its time to back down.
And I said the other respondents saved me a lot of typing. God help us if they'd not written first...
Cheers,
Rex
Summed up: Get a chronograph.
