Hiya Jack.
Sounds like your having a bit of a nightmare mate.
The obvious one's that come to mind......are the pellet's clipping the moderator?
Try taking it off and gently tapp it on some white paper, see if there is any swarf.
Sounds like you have checked the rifle screw's etc.
Re the Scope, yes you can dammage it if you tighten the mounts too much, you can crush the tube, and damage the reticle.
I know some dont like cleaning the barrel, but it may be worth a try, then led it back in, and try again.
Could be you mate, poor body position, and head position is favo