This week I installed a 12 FPE Vortek tune kit in my TX200 (.177 Cal). The gun in stock form was shot about 15 to 16.5 FPE, which was a little too hot for consistent accuracy, and restricted me to shooting heavier pellets to keep the velocity below 900 fps.
At any rate, I installed the 12 FPE kit, along with the included piston seal (my OEM seal was cracked) and one spacer between the piston and the top hat. Very easy to install: However, I could only install one spacer, since the gun would not cock with 2 or 3 spacers. My target was to get somewhere between 11.5 and 13 FPE from my rifle. Here are the 10-shot chrony results from the two most accurate pellets (JSB 7.33gr and JSB 8.44gr) after about 150 shots on the new spring and piston:
High: 880.2 fps
Average: 870.0 fps
Extreme Spread: 23.8 fps
Stand Deviation: 8.31 fps
Av. Power: 12.3 fps
High: 820.6 fps
Average: 813.3 fps
Extreme Spread: 12.2 fps
Stand Deviation: 3.31 fps
Av. Power: 12.4 fps
I anticipate that the spread will decrease when the spring and piston seal are fully broken in after about 500 shots. I also anticipate that the velocity will drop a little, but I should remain in my 11.5 to 13 fpe power target.
What these chrony numbers don't show is the improved accuracy of the rifle (see attached target). I am consistently shooting dime size groups out to 35 yards and dime to nickel size groups out to 40 yards. No more 'BONK' sound during the shot cycle, just a pleasant, short 'snap' sound. No more drama in the sight picture: The recoil is greatly reduced and the target remains in the scope through the shot cycle. And the gun is real easy to cock at about 24 lbs: This old guy can shoot this all afternoon and not get tired.
If your TX200 is shooting too hot or harsh, you might want to give the Vortek 12 FPE tune kit a try.