Wolverine 2 .177 issues

I am writing on behalf of my Father in Law who bought a Wolverine 2 a few months ago. I was wondering if anyone else has a problem regarding 1 huge flyer in every magazine, Daystate sent him a 'replacement', built under supervision of their boss but using it today the problem still existed...a really good grouping at 35 yards within the space of a penny but always one that was 4 inches away. Open to suggestions but please bear in mind he is a pretty good shot and has tried different pellets etc. Just wondering if anyone else has the same problem?...cheers
 
Stu keep the barrel oring in mind as well. It's an outside chance but if you get same results from single tray I would change the oring next. .177 is a 4x1.5 mm NBR70 oring on the wolverine 2. The daystate mags don't apply pressure to the pellets like most spring mags do so if it is the mag there are videos on YouTube on how to disassemble that are very helpful.