FX STX Superior LinerThe groundbreaking Smooth Twist X barrel liner has been further perfected. FX Airguns proudly introduces the new FX Superior Smooth Twist X Barrel Liner (or FX Superior STX). The new Superior STX barrel liners are still created using the patented way of pressing the rifling into the barrel from the outside; but this is now done with a higher degree of precision, lower tolerance, and some other slight modifications that result in a superior liner to