FX Crown is really a great gun , for sure . I must say that mine has some POI shifting problems . I' thinking to tension the barrel the same way Ernest Rowe did.
But now I'm wondering if using a 380mm barrel instead of 500mm would fix this problem as well , without lost of accuracy. Does your Crown have a super lite barrel? If it does according to Ernst, the barrel sleeves won't work. I emailed him to ask for specific sleeve installation for the CMK2. He responded within hours, hats off to you Ernest!
I'm guess because the sleeve is slightly larger than the supper lite barrel. I tried one on my 600mm barrel and it slid right out , not even close to snug. No change in the grouping maybe a tad worst. I'm am planning on wrapping Teflon tape around the barrel in 3 locations corresponding to where I'm putting oring spacers. Time will tell When do you notice the poi shift? Have you tried a different scope? So stats and photos would be helpful.