^
In other words, what does velocity tell me about pressure?... and is velocity a fool proof way to indicate pressure?
Not really. You can load a low-velocity load with a fast burning powder and wreck the gun. Just think of loading 20gr of Bullseye in a .308 case. You won't get much velocity, maybe around 1500 f/s (just guessing), but the pressure will be enormous, probably blowing the primer, if not separating the case and possibly cracking locking lugs. An extreme example, of course.
Just remember that pressure goes up exponentially with loading density, but velocity does not. There are too many variables including burning rates of different powders
at different pressures, quality of barrels, etc.
While the only proper way to measure pressure is with a pressure barrel, there are some field indicators for you and me to tell when pressures are getting higher, including degree of flattening of the primer, piercing of the primer, and, back home, measurements of case head expansion, bright shiny rings around the base of the fired cartridge, stretching of the case, etc.
And all these things are subject to component variations, like hardness of the primer metal, case volume, whether the bullet can get pushed back into the case on feeding in certain guns, etc, etc, etc, etc, etc.
Mere velocity won't cut it hardly ay-tall.
While modern rifles are pretty strong (the M1 Garand will take 125,000 "pound" blue pill test loads), there's no sense possibly making every round a proof load for the sake of a couple hundred f/s.
Stick to published loads with published components*, and remember that some loading data is less aggressive for reasons which have been arrived at
not only by lawyers, but also by experienced ballisticians with expensive actual honest-to-G-d pressure measuring equipment and instruments.
And probably degrees in physics.
Terry, 230RN
*Sometimes this is impossible because of component availability... which is another reason for "conservative" loading data published by the Big Boys like Hornady.