I'm afraid I don't understand the infatuation with "P&R".
Pinned is what has long since been proven to be an unnecessary version of "belt and suspenders". Recessed came to be in the 1920's when (Remington's) .22 Long Rifle ammo was blowing rims. Both Remington and S&W (and perhaps others) set out to solve/mitigate the problem.
Remington went one way, and S&W went another. The seeming difference in their respective approaches was Remington's folks must have been to Problem Solving School---where the very first thing that gets beaten into your head is to make sure you KNOW what the REAL problem is---before you spend valuable resources trying to solve symptoms of the problem. They stopped buying cheap brass, and the problem was solved. S&W moved heaven and earth, and came up with the recessed chamber (in the Straight Line single shot----first ever handgun with a recessed chamber)---which achieved the dubious distinction of increasing the difficulty of cleaning the gun-----then AND now!!
Perhaps someone can explain all this---then again, maybe they can't!
Ralph Tremaine