I have just bought a new .22 hw100kt. Using h&n ftt individually weighed at 14.5g it is shooting 589 to 599fps over a full fill giving 90 shots. I hope it drops a little.
Accuracy wise at 25 yards average group sizes are 4mm ctc. It will basically one hole. At 35 yards its 8mm ctc and at 55 yards 12mm ctc on average.
Accuracy drops off after 350-400 pellets but a quick vfg felt pulled through with barrel cleaner has it straight back to normal. It does seem to get dirty quickly it might be better using 5.51 pellets more so than the 5.53 h&n ftt pellets but they shoot so well I don't mind cleaning it every tin or so.
Hope you get yours sorted.