Spent the afternoon having a plink with the '50's Diana, as above, a Webley Junior rifle from the same era, & a late '60's Falcon. Instead of just can blatting set up some proper targets @ 15 yards.
Given my limited ability,was pleased with the groups.
Only problem - the 25 had to have it's sight ramp on close to max elevation to group on the bull.
Tried it with Hobbys, Excite 2's, Bisley Practise, even SMK Shitefires. Much the same.
Checked stock screws, no barrel droop, power seems OK - original bueing in good nick, possibly a refinished stock, good breech seal.

Wondering if the 'leaf' on the sight has been slightly bent accidentally, & to bend the tang up, very carefully - holding it near the pivot of course!

Any advice welcome

Bru