I thought I let you know my latest results and also ask if other people have had similar experience.
I bought
this ammunition by Sellier&Bellot recently, since there is absolutely no Winchester Ammunition available. I was a bit afraid due to my bad experience in the past. However this stuff worked absolutely GREAT in my 1970's Mauser. It is a bit picky with Ammo and I usually have some malfunctions, although, after GT fixed my magazines and brought me from 1 up to 5 working magazines

it was better.
GT if you're reading, even the one magazine that still had some problems worked without any jams.
Out of 50 shots I did not have one malfunction. So I think that this stuff is better for my gun than the Winchester White Box. You might want to give it a try.