Sherman Bell compared the location of peak pressure between smokeless and black powder (4 different kinds of smokeless), and loads ranging from 1-1 1/4 oz, in "Finding Out for Myself, Part VI: Smokeless vs Black". Double Gun Journal, Nov 02. He used strain gauges at the 1 inch, 3 inch, and 6 inch marks with others farther down the barrel. They all showed the peak pressure at 1" from the breech, with drops of at least 1,000 psi by the time they reached 3". Smokeless powders used were SR 7625, Clays, Universal Clays, and Blue Dot. Even the FFFG black powder--which some "experts" suggested would peak farther down the barrel--showed a significant drop in pressure by the 3" mark.
JRB, as Jones pointed out, there is no direct conversion from LUP to psi. A rough "ballpark" formula is: LUP + 1,000 = psi. If you build in some cushion when applying that formula, it's close enough for government work.
