HW97Kt and a Vortek PG2 SHO Tune kit

Here's my take though I'm no tuner-I did rebuild my R9 with a Vortek kit and the help of a buddy who took a 2-week course from a Randy Bimrose who used to work as a smith for Beeman in the glory days. In my buddys' opinion the Vortek kits are more of a drop in with the piston seal rarely needing to be sized to the compression tube. The washers are indeed there to adjust your preload and power. You can leave them out entirely if you wish, or try various combinations to see which yield the power and shot cycle you're looking for. My Beeman R9 was apparently a rarity as it shot with a solid 'thunk' right out of the box. The Vortek kit will give you a nice twang-free shot cycle.

I rebuilt my R9 after maybe 6000 shots as it had lost power (though it still shot accurately) When we tore it down it turned out I had a 7 piece mainspring!

ALWAYS refer to maker for specifics, who would know better than them? As to the seals I have had to size the Vortek seals every time, making them oversized would make sense as size can always be reduced but never increased.

These are drop in kits and function very well for smoothing the gun’s shot cycle. As for as power increase, none of the 3 I have installed in any of my guns have produce more power. Just a smoother shot cycle which made the guns more accurate. Hope this helps. 

I installed mine with no washers and it worked perfectly. If you get too many washers, you probably will not be able to get it fully cocked.