All of the above info is good. Don't forget that a gun with even a little excess headspace can give high pressure signs with your primers, while in fact there aren't any pressure issues at all. Variations in primer cup hardness can also give different appearences in the fired primer's appearence.

Trying to read pessure without a chrono and published data, or a pressure barrel, is futile at best, and can be dangerous at the worst. In days long gone by, they didn't have all the chrono's and pressure barrels etc., that are available today, and they tried to figure pressure the best they could, even though most of it has been proven totally unreliable today.