As I mentioned in my post, original Kynoch 470 ammo drops into the chambers perfectly with no dramas.
Also OLD BELL formed cases also drop into the chambers perfectly.
This would indicate the problem is not the chambers.
The dies are definately at fault as a case formed in the full length die ends up with the shoulder a long way forward of a Kynoch round.
Actually the shoulder is a full 160 thou further forward than Kynoch and OLD BELL!!!!
The tightness does not occur at the base of the case.

The bottom line is that the ONLY cases which are tight are ones formed in those dies.