Damascus,
Thanks for posting that photo. I had the identicle problem with an old American gun, and posted about it, here, but, I had no photographic evidence.

The cure for my gun was a simple lengthening of the forcing cone, NOT the chambers. The cones in that gun were rather short and were more like "steps" for lack of a better word. I did have regular posters, here, reply that they doubted what I was describing could actually happen.

Best,
Ted