You FX comes apart just like a Prohunter XT does. Just take the 2 forearm screws out and take it off. Then just tap out the hinge pin. Look up Dissembling a TC Prohunter FX there is a YouTube video showing you how to take it apart.
The only difference between the FX and XT is the frame. The XT frame has higher tolerances on dimensions and how it’s made. That’s why it cost more and you can swap barrels.
The lock down spring can make a lot of difference in how tight it locks up and how good it shoots. The factory spring is like 30-32lbs and Mike Bellm at Bellmtc.com sells a 51lb lock up spring for about $9 bucks. It takes 5-10mins to change and you can find a YouTube video showing you how to do it. The Hinge Pin is also important. You should have to tap it out with a small hammer or mallet it should be tight. If it’s loose enough to move with your fingers then you need a oversized Hinge Pin. Bellm sells those also.
When you put your gun back together use a little lithium grease or oil on your hinge pin to tap it back in.