The new FX Airguns Superior Smooth Twist X Barrel Liner. Produced in the FX patented way; by pressing the rifling into the barrel from the outside. But now with a higher level of precision, lower tolerances and more tweaks, resulting in a superior liner. There are two types of liners being released for most calibres; a standard Superior STX Liner and a Superior STX Heavy Liner. The standard FX Superior STX Liner can shoot a standard weight pellet and Hybrid Slugs, maximising the accuracy of the FX Hybrid Slug. The FX Superior STX Heavy Liner will be replacing the STX Slug A liners in the coming months. Heavy denotes that this liner has a different twist rate better suited for heavier pellets and heavier slugs (as opposed to lighter weight Hybrid Slugs).