I had an fx royal that would not group at all. As i was going to use it for hft so i made a single shot adaptor. When using the adaptor it grouped very very well so the problem was found to be in the magazine. I think FX make a generic magazine that has to cater for normal guns and their automatic variants. The automatic variants need a mag that will operate fast and efficiently in an auto so I think they just beefed up the mag rotation spring. I did some tests by loading a pellet via the mag and then removing the pellet from the breach with a rod from the muzzle end. I found quite a few deformed pellet skirts so the mag is the culprit
The solution was to weaken the spring in the mag. Accuracey restored. hth