I'm wondering how much you you shot it before you decided the FX 500 shot better.
Also, if scope is perfectly level, optically centered perfectly, and aligned perfectly with adjustable rings. All of that 1/3rd degree off makes a difference in tolerance stacking at various distances.
Also, I'm wondering about pellets used. We're told to clean a barrel when we first get it, break it in, etc. Most guys don't clean & season their barrels for a different pellet.
There's a lot of things that could have had it below your expectations. Not impossible, or hard to say one thing without talking to Alan.
I personally miss my English AZ Rapids in .22 & .25.
If buyer who bought the .22 for Wife ever wishes to sell it back, I'd pay what I charged you.
If buyer of my .25 that was sold on by a G.F. out of Pennsylvania ever wishes to sell it back to original owner, I'd discuss that option.
PM me if either ever read this. Actually, if ANYONE has any Rapids Made in England they will sell, any caliber, please PM me.