Well, having now examined in great detail I cannot see how the release tab is the cause of the problem. I believed we were on to something, but NO.

All I can see at present is exactly where and how the jam occurs but not why it happens.

In the absence of any other material factor being evident it seems I have no option but to polish the feed ramp to the smoothest feed possible.
Truly I hate this idea because something has changed from when the rifle was built to cause this problem, but I simply cannot identify what.

There are some on this forum who have been very helpful and I appreciate that.

Any further thoughts are of course welcome as I have not taken any action yet other than investigation.
Cheers, deeangeo