Thanks for responding, 100% agree, no pressure signs on the primer, just lots of marks on the bottom of the case. He tells me the Bolt is quite resistant to close before firing on these particular rounds. He is going to try and re-chamber some brasss after work this evening and see if they are still chambering correctly. I know he also has some hornady brass so will see suggest he fires that with the same load for comparison.
Fortunately, there is no swelling of the case. a bit more testing and development is required i think.