I’ve got a set of RCBS 9mm Luger dies that I’ve also been using to load 9mm Largo, and rather than reset the dies every time I switch between them I’d like to find a spacer washer that I could put under the lock rings when loading the longer round. This is the same sort of spacer that’s usually supplied with die sets that double between .38 Spl & .357 Mag, or between .44 Spl & .44 Mag. I’ve measured my own fired case lengths and the Largos average about 0.15 inch longer than the Lugers I’ve collected: Starline’s 9mm Largo cases run 0.892” after firing, and Winchester’s Lugers run 0.741”. So it logically I need do find a washer that’s 150 thou thick, assuming I load the same bullet in each, which I do: Berry’s 124gr plated round nose. (Both pistols are range toys, not serious tools.) I measured the spacer supplied with my RCBS .38/.357 dies and at 0.127” thick it’s way over the 1/10 inch you’d expect from knowing that the Magnum case was specified to be a tenth inch longer than the Special. So what gives? The (former) engineer in me says that extra 27 thou is going to clobber any precision I might pretend to (never mind using bullets with different ogives). Am I obsessing about the trivial, or missing something important?