Thanks for posting the vids, unfortunately when I owned my HW77 there was no internets (it was a while ago!) but I would have loved to have had a fettle with it. I did think about it but didn't want to brake it as repairs would have been a lot of pub work to pay for it.
Only thing I fettled was my Gat pistol, even a basic trigger and piston polish helped a lot but you know what they say about a sow's ear...or polishing a !
I ended up fettling, tuning and in the end designing and building mountain bikes (and components) for a living. Perhaps my next rifle will get "the treatment"