Kuduae, thank you for confirming that. I had a look at the rifle again this morning and noted the front action screw is in line with the barrel thread and had assumed there was a good chance there was a screw/barrel interference.

Today I had a few minutes spare so the bolt and magazine were stripped and cleaned. It would appear the barrel at least has been re-finished at some point and I suspect the bolt and receiver possibly as well as the pistol grip plate is colour case hardened whereas the rest of the rifle is blacked.

Would the flip up cover in the pistol grip have been used to store the front sight hood or some other purpose?