FX WC Wandering POI, penny for your thoughts.

Take put the free flight hammer and spring (note spring direction orientation) etc and clean inside the tube and all parts and Try flip that spring around. Who knows you might have lead dust or shavings or pellets inside causing the erratic behavior.

This, I believe would be manifested as a variance in speeds. The speeds have been very consistent so far after I put on a Huma reg in it. 
 
Probably just me, but I think all the discussion about torque settings is kind of extreme. I've had my Veteran apart several times, and just screw it back together by feel, never measured torque value on a single screw, and it's always perfect. Yeah, I've turned a lot of wrenches, and my feel is pretty good, but not perfect, I'm sure. I'm probably wrong, as my wife would agree, but if you look at the FX design around the barrel assembly on these rifles with liners, it is frankly amazing to me that they aren't all problematic regarding POI stability. Too many parts and too many places for error. On the other hand, if you like to tinker, FX offers a lifetime supply of opportunity. For the most part, my rifles either shoot, or, the barrel is dirty, rarely any need to look further. I like simple. 
 
I would need a proper spring. When I upped the reg to 120, speed actually decreased. I don’t think the spring could keep up. As it is right now, I have the 8.44s moving at almost or just above 1K fps. The monsters actually shot really well at some point at 750fps.

At any rate, speed/power isn’t the problem. The gun will shoot accurately. The problem is it’s inconsistency, that accuracy is fleeting. POI changes, etc. 
 
I affixed a Carbon Fiber liner on it. But before I did that there were 3 O-Rings in place being held by Teflon tape. It’s a 500mm barrel. 
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What did you end up using to bond it to the liner? Id still slide an o ring on each end of the carbon fiber tube. How much are you tightening the liner nut? I just barely snug mine up.

The o rings in the clamp that the liner sleeve slides through, do they feel like they are fitting snugly?

Im about out of ideas. Before running over it with a truck....id probably spend the $10 or so and replace every o ring in the liner system and put some 90 duro in the clamps.
 
If you haven't tried yet, ive heard of guys giving the muzzel end of the liner a couple wraps of teflon tape before tightening it up.

Will give this a try. Probably the last thing. Will be shooting some reviews for my channel & will list it with full disclosure in a few weeks. I have done it all, every O-ring has been changed, have run out of ideas myself. My HW30 can out shoot this Wildcat at that distance. 
 
I would do what Rj said about the liner, orings and Teflon tape. I also would not give up until I replaced the orings in the clamps that support the barrel with some NBR 90’s. I went back a read what you said from the beginning. You are running the slim pickle look because your shroud causes you even more grief. This is a big clue to solving this riddle.