Just for completeness for anyone searching threads in the future.
Situation has been resolved with a very tight rear bushing, as in just contacting.
As soon as the bushing was put in, rifle was shooting tight groups at 50m - bang on a target - was 1" high at 50m without suppressor.
I'll lift it slightly, but very impressed with accuracy now - and shout out to the good guys at GCity Wgtn that gave me the bushing to sort it out.
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