Thanks for the suggestions.
I'm on that Luger Forums and have posed the obvious question; what do they require? To which the answer has been ( more or less); 'They are like women, there is no answer'
I have tried 1.125 through 1.160 with velocities from 900 - 1200 fps; all FMJ 115 & 124 weights. I've both style of magazine; coil and zig-zag (term?).
There is no magic bullet that I've found; it'll work for a period, then...FTF. Which is par for the course; if I read correctly it's the steep angle that is the start of the feeding problems.
Aggravated of course by the fact that my other period piece has a next-to vertical magazine; so it'll eat anything, with aplomb.
I've said it before..."Lugers are like a stripper GF. Everyone ooh and ahhs over her lines, wants to handle her and blow all kinds of Sunshine up your *ss about how cool she is...then she squats and pees right in front of God & everybody! Nice..."
But they are cool pieces. This one is a mismatch, but is so well fitted that it's got to be a factory job. The toggle is a mismatch.
It's a 1941 made Mauser, but not the 'BYF' version.