No 1 MK 3 rebuild, possible bedding issue

[Son]

Dave, you sound like you know what you are doing- so here's a possible quick fix. Can you make a spacer, probably start with something under a mm thick, like a tiny washer. Fit it on the thread end of the inner band screw and make the outside diameter the size of the large diameter of the screw. This will extend the length where the spring sits and may relieve the band enough to give it free play in the wood by Mr Horton's test and stop the barrel being pulled down hard.
The barrel should have contact in all the points I described earlier without the band tightened, what you need to achieve is when tightening the band you are not moving the barrel.
Then do another testfire.