fx barrel liner is a system where interchangeable barrels have a thin "liner" which is the rifled bore which fit inside an exterior housing or "barrel". It offers a system where you can swap out twist rates in a pinch. 1:24-1:18-1:16... @ $109 per liner. You'd buy the liner housing or "barrel" and liner lock/TP-liner receiver, outer housing which would be the Outer diameter of the stock Zelos barrel and fit in its place.. and muzzle plug/liner lock nut which is the housing/receiver of the muzzle end of the liner. I don't know that it would be necessary unless you want a Longer or shorter barrel. the stock zelos barrel is Extremely accurate in my experience, and most who i've spoken with. You're going to spend about $250 on the FX conversion kit and and the liner you want to use. Top pic explains the Liner barrel system, bottom is the Zelos Kit.
View attachment 553489View attachment 553490View attachment 553493 As far as how... it's just a barrel swap.
Bottle, Aftermarket High flo TP, Porting. Talk to
@Firewalker for more.