I have been on this journey recently. I get the gun brand new and it was shooting almost bang on 6. Immediately stripped it down and fitted a tbt kit. It nicely sat at 5.3. Fitted the Aussie seal and it went back to 5.9. I then fitted a polish seal and it was sat nicely at 5.5, but power started to drop to 4.9 after a tin of pellets.
I stripped and cleaned the whole thing and fitted the aussie seal again and now it is constant 5.75 with RWS hobby pellets at 11.9.
I have learned a few things here. There is definitely a bedding in period for the kits and the seals.
The Aussie seal is best for consistency.
It is frighteningly easy for these guns to go over the limit. Get a Chrono that does a full breakdown of the reading like a LMBR not ones that round up and down like the Athlon.
Once mastered they are deadly accurate right out to 25 yards.
The recoil destroys sights and red dots. I swapped out to a £300 holosun multi reticle (I have an astigmatism) and haven’t looked back. Worth every penny.
I now have a Welsh Willy kit to fit in mine and also another HW45 in .20 on back order.
I absolutely love mine, but it took some serious messing about to get it where I wanted it.