I have a kit bought from Dave, pack not even opened.
Described on the pack as for HW77 and 97 , 26mm, 0.177 and 12ft lb
Cost me a grand, you can have it for the same.
PM if you are interested.
Swordfish the kit will smooth out the whole firing cycle. Reducing recoil and improving the locktime. It's hard to explain. It just makes the rifle a lot more pleasant to shoot. It will also quiet it down because it has a very tight fitting spring guide which completly eliminates spring "twang".