JSB Monsters and H&N Rabbit Magnum II in 22 cal, Accuracy in FX Royale's

Has anyone tried these pellets with success in an FX Royale.
​If so were you able to get suitable groups for hunting.

​Yesterday we tried a Royale 400 at 720 fps and a Royale 300 at 730 fps, groups were in excess of 24" at 40 yards, the pellets could be seen spiralling wildly, many missed paper completely.
​Both rifles shoot sub half inch at 50 yards with H&N Barracuda Match and JSB Heavy pellets.