Originally Posted by Tench
Another job on the list of things to do when a rifle doesn't group after cleaning the barrel is to replace the breech seal, a leaking breech will make a rifle shotgun! So try that next.
Yep, on my old Harrier X2 the group size went completely to pot due to the o ring on the pellet probe being slightly damaged. I couldn't see any damage by eye but Daystate sent me a some for free, it took a few minutes to replace and the group size went from over 30mm to a raggy hole at 25 yards instantly. I can't remember the size but no doubt someone will be along in a minute to confirm what size to get. It's such a cheap and easy thing to do so try it before you start stripping things down. If it doesn't work you'll be less than a Euro or two out of pocket. Get a few and change it annually for peace of mind.
ISP Airstream MK III No 15 which is a bit poorly at the moment and having a rest
AA Pro Sport + Ginb FT8 stock + Bushnell 4200 6-24x
EV2 MK1 + Leupold Comp 40x
Weihrauch HW100 KT laminate
SBFTC Competition Secretary