You might want to check out airarms hunting SA on you tube who reviewed the US extra Fac ,and whilst the 12ft lbs version is a great rifle, the US extra has limitations on usable shot count. You will see what I mean when you see the graphs on the video.

I fitted the vortek kit myself and they are great kits, any twang removed, power upped to 11.5ftb but recoil reduced. Perhaps more importantly the gun is now very consistent with a spread over the chrono of only 5ft/s over 10 shots . And all this with no top hat fitted as per instructions, I must ad...