The standard spring is sloppy on the fixed spring guide (only the first few thousand sussex armoury models had a separate spring guide) but there is plenty of power potential there, the simplest way to tame them is use a narrower spring that is tight on the guide as Jon said, this leaves room for an extra liner as well as the original factory black one, make sure you fit a new o-ring (make sure its the correct imperial one not a metric) and that the tap isn't leaking and that the barrel is nice and tight in the action - all this reduces the slam. pellet choice can effect power by a couple of foot pounds as well as keep the slam down, I find superdomes the best all rounders for AA sidelevers.
I recommend against playing with the spring guide or polishing the piston, due to the nature of the sear engagement and non hardened parts any play at all back there will produce a dangerous light engagement.
HTH
"But we have our own dream and our own task. We are with Europe, but not of it. We are linked, but not comprised. We are interested and associated, but not absorbed."
Winston Churchill 1930
Wasn't the point of the Sussex Armory/AA plastic fantastic to be LOUD?
"My gun looks modern, and sounds more real than yours " "Those plastic toy soldiers are going to get a bad day"
I'm surprised it didn't come with a bayonet; the Airfix one did.
Put about 100 pellets through her today and she is really shooting well now ! the foam in the stock has 100% killed the plastic sound box noise. I liked it, but love it now they should have spent a few more quid at design...it is so close to being really good!!
Anyway teenage yearning to have one now satisfied
I remember bringing my AR7 (Combat) to a HFT shoot years ago. People thought there was a rimfire on the course until they realised it was me 😁
Lovely airguns and sounds you are loving yours 👍
Regards
Paddy
BE-HAPPY-OK