Yes,
I did one a few years back.
Easy enough. The slot is very very rough and could do with a file.
It’s very easy to go over power as the 300 and 400 were made initially to run at higher lower levels and de tuned for the uk.
I used a standard spring from chambers, re lubed and filed the slot and was on 11.4 before it settled.
Very simple to work on, but it can be easy to round screws.
Chambers has an exploded diagram that may help you.
Regards,
Rhys
Theoben TTR1 .177, Steven B Blue/Grey Laminate Stock, Nutshot Mod, Hawke Sidewinder 10x42 Tac IR
Daystate Pulsar. 177, Donny FL Sumo Mod, Pard NV008LRF