Just a quick update.
Out the the stock and chrono'd. 3fps spread over 10 shots, so all ok there lol.
Turned power down to my preference of 11.2 with 8.4g pellets. It was up at 11.7 originally.
Bloody good clean of the barrel, way more than I've ever done before.
Back in the stock, check everything over and tighten everything down.
New tin of 4.51 AA Fields. 4 shots to zero, then one tiny tiny 5mm hole lovelyness
this is only at 28 yards as it's as far as I have in the farm that's sheltered. But my god it's good
thanks for for everyone's help!!