Thanks both for your input,

I took the action out of the stock and found that there is still a gap between the mag well and the receiver even when the long screw behind the trigger guard is tightened to the last. Maybe this screw is too long and even if it would not bee too long there meight be not enough space in the stock to tighten it correctly... On the other hand, the follower has some side play left and right when there is no round in the mag AND I press mag well and receiver close together to simulate a tightened rear screw. And even then, the last round pops out. I guess I should try to shorten the screw or should I first try out another follower/spring?

best regards
Ulrich