Thanks for the replies.

Pretty sure it's still settling down, it's only fired 50 or so since being put back together.I'll certainly try Marksman again & probably keep it on Hobbys for a while. Haven't got any of the Webley pellets but might invest iin a tin based on the comments.
Also I'll have a look at a spares diagram.....fibre washer? Never came across one of them, perhaps it disintegrated. Certainly worth a look even if it turns out to be a mod on later models, might be able to incorporate it on ths one, cheers. Would. E nice to smooth/DRP the cocking effort.
Might be wrong but I can't see this one doing 40mm at 40yds, only one spring for a start but it would be nice to be to shrink the group size at 15 yds. I put it away & tried something else to check it wasn't me....