Help FX wildcat.25st can I upgrade this?

No you can not drop a liner from a different cal into your gun. Also both cal must be same length. Example your wild cat needs to be both .22 cal and 700 to accept a .22 700mm liner. You can not drop a .22 700 liner into a .22 600 barrel. And you can not drop a. 22 liner into a .25 cal. Doesnt work that way. Fx/airgun depot already mention this many time cause people think they can drop any liner in length to any cal they want. Dont work that way bro. Get the whole barrel kit if you want to change cal or length. 
 
I had the same thoughts after the STX guns first came out. I called a reliable FX dealer, even FX themselves, and both said it couldn't be done...at least in the traditional sense that you're speaking of. Of course you could always take an STX barrel liner and build it up to the right size with precision metal tubing or CF, do all of the other threading and drilling required but I'm not sure it's worth the $$ or trouble? My MK1 .25 Cat with the original smooth twist barrel is doing a wonderful job with 33.95's around 845fps at ranges where Impacts and Crowns normally live. Those guns are prettier and more adjustable, might even print groups that are a teeny tiny bit better but from where I sit...I don't see anything that's pushing me to upgrade barrels or guns right now

Glenn in Texas