I too have experienced this with a silverline 97 kt that I bought new last year.
The Zero would shift down and left about 10 clicks and then move back randomly, good groups but in different places .
I tried a lot of things, changed mounts from BKL 2 piece to a sportsmatch one piece , still did it.
Changed scopes , still did it.
The final thing I tried was to fit a Sportsmatch droop mount . Unfortunately the mount I had ordered wouldnt fit my bigger scopes as it was a low version, so i had to fit a 6x AO scope and surprisingly it held. It kept on holding for weeks , then months . Now i have bought a high droop mount and its still good with a 6-24x44 Nikko stirling nighteater on it .
I can't explain the physics behind this , and it was still cold when I first started experimenting with the droop mounts . I suspected it to be a mechanical movement of the tube with temperature but now it doesnt seem to do it any more . I could go back and refit all the old mounts and scopes and see if it comes back , but its shooting well at the moment so i'm going to leave it and use the gun for a while . It matched its best score today at my field target club , 4 points behind my pcp shooting friend .
I use crosman premier 7.9 pellets . The gun has never been apart , its got factory internals .Its probably fired around 3000 pellets from new.
I am just about to get a 77k, this will have a Welsh Willy kit fitted with Krytox from new so it will be interesting to see if that behaves in a similar fashion .
Last edited by Skengy; 5th July 2015 at 08:25 PM.