Thanks, NCsmitty.
Actually, I made that discovery too, but my troubles have persisted. I'm using PPU headstamp brass (the Privi Partizan ammo I bought soots the cases terribly, and hits pretty inconsistently, problems I didn't encounter with their ammo for the 7.5x55, but the brass is good, as far as I can tell. I'll probably pull what's left and reuse the primed brass with Hornady 140gr soft points).
I like the theory of uneven powder measures . . . but I've been weighing each charge--which takes forever but which I thought would keep everything consistent. (I use the Lee powder scale, along with a powder trickler made from a business card and a wooden coffee stirrer).
Anyway, today I bought some H4831SC, and will run up some loads with that in the next few days (hooray for Spring Break!). I'm hoping that the slower powder will solve this weird haunted-Mauser problem.
Meanwhile, perhaps I should confess that I just had venison for lunch--from a deer I killed this season with one of the reloads I'm fussing about here.
Will keep you all posted. Thanks again for this--and all the wisdom I've gleaned in my visits to THR.
--ProfessrH