The FX'S are very serious and extremely well made rifles.
They are the cat's ass.
I suggest you watch some of Ted Bier's "Ted's Holdover" videos on U-Tube. Hr actually did a video on the over stability of the waisted pellets in the FX Royal, I think it was.

One of them was about the over speed of some FX rifles.
This causes inaccuracy at extended ranges due to the pellets girarion around the point of aim.
The FX rifle should be adjustable and adjusted to give about 960fps. This speed or slightly lower will give excellent accuracy to in excess of 200yards with the heavier of the match pellets.
I suggest the 19.09grm H&N Barracuda as well as the 22gr. H&N Match. JSB pellets will also shoot well, maybe better than the H&N's.