Don't forget when we are talking of minimum thickness here we are primarily speaking of the thickness in the forward third of the bbl. Max Chamber pressure plays a very small role in what the pressure in the bbl is down there. "IF" one fires two different 1oz loads having equal velocities, one giving 6k- pressure & the other 8K+ then after about the 3" point in the bbl is reached the load having the higher pressure will now have the lowest.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra