Hi gents first post so be gentle with me. I bought a brand new challenge hft 10 days ago and a swfa 10x42 to put on it. I was extremely happy with it when I set it up. I found some pellets that it really likes (webley acupels) and was getting 5p sized groups at 40 yards shooting off bags. I shot a course at my local club on Sunday and couldn't knock anything over so I shot at a face plate at 20 yards and it was shooting low and right about 15mm (zeroed at 30 yards). I had monday off work and spent a few hours at the plinking range to try and work out what was wrong. Before shooting I gave the barrel a thorough pull through and re zeroed at 30 yards again. Everything was going great again for about a fill (200 bar down to 100) then I was getting poi shift again, first high and left then after re zeroing low and right by about 20mm at 30 yards. It was grouping just as good as before just the poi was shifting every so often. I then put a couple felts through it and it seemed to stabilize again. From this I can only assume that it likes a spotless barrel? The acupels it likes are a very dirty pellet, they leave a fair bit of residue and dust on your fingers after handling them. I don't think my issues are temperature related as it couldn't have shifted more than a couple of degrees over the three hours or so I was there. The wind was also only blowing at about 2-3 mph so I don't believe that had much of an effect. I thought that it could be the new scope but it seems solid, however I haven't tried it on another gun. Obviously after spending over £2500 on my new setup I'm pretty frustrated. Any thoughts or insight into this issue would be greatly appreciated. Thanks.