Many thanks to all for your comments.
I tried different loads from the Vihtavuori Reloading Guide, because there are loads for exactly this Hornady bullet. And also with 6.9 grs N340 I have this problem. With this load, I believe the slide will move back the full way.
I have another idea what is going on:
When the bullet hits the feedramp with to much speed/force, it's more bouncing off than sliding the ramp along upwards. That does mean that the angle of the round is too steep. The bullet nose hits the upper part of the chamber, and the brass (where I found the dent) the lower edge of the chamber. This point works like a pivot when the slide is moving forward, and the whole round is turning around this point. The bottom is now moving down/forward and the nose will go up/backwards. And because the nose has contact with the chamber, it can´t move and the gun jam. What do you think about that theory?
To check that, I did the following:
The original recoil spring is a Wolff Longslide spring #3. The Longslide springs have no ratings in pounds, they are rated in Numbers from 1 to 5 and must be fitted to the gun. Detlef has recommended a 16-18 lb spring. So I´ve taken a Longslide spring, have cut and measured it until the strenght is equal to a 18 lb spring. But now it has the lenght of a standard (for 5" guns) spring.
Now a question:
if this works, is it realy necessary to use one of the Longslide springs, (lighter, but as long as the original one) or should I use in the future a spring in standard lenght?
Tomorrow I make a test with the adjusted spring at the range, and I post the result.
@ Carlos: I will stay with the SWC, because the gun shoots the tightest groups with them. They make also this nice looking, sharp edged holes. And you are right, I want to know the cause of the problem and solve it. In the meantime I used RN at competitions.
@ Detlef: Wie klein doch die Welt ist. Da finde ich ein amerikanisches Forum, in dem es eine genau passende Rubrik fuer mein Problem gibt. Auf mein posting bekomme ich dann auch eine Antwort in Deutsch!
Taurus