So a chronograph is an indirect crude way of measuring pressure... But the average joe staring at a piece of unknown brass isn't??!!
Where do we get velocity out of the bullet from, if it isn't the pressure behind it?
The fact that various rifles show different velocities is due to the varying manufacturing tollerances I spoke of, in production rifles.
When you are only matching charges and your velocity exceeds book values, it's because you are using the same thing as the book. It is possible that you have some tight tollerances, but not likely. The reasonable explaination is the different lots of powder(tested, Vs. what you use), when you burning speed is faster, you have higher pressures.
Denton has shown rather clearly that the "powder" isn't quite the devil you think it is, when it comes to temp stability. Here is one of his articles.
https://www.shootingsoftware.com/ftp/Pressure%20Factors.pdfAnd a few other articles you may find interesting.
http://www.dtic.mil/ndia/2007smallarms/5_8_07/Webb1.pdfRead what they say about "universality"
http://www.accuratepowder.com/faq/
