FX STX Slug Liner A, 600mm, .22 caliber Compatible with FX Crown, Impact, Wildcat and Dreamline models with STX barrels The first Smooth Twist X Slug barrel liners designed by FX have been developed around the Nielsen Specialty Ammo line of precision hunting slugs, picked due to their high marketplace demand. These liners will work well with any quality slug made to these specifics, along with the correct regulator/hammer setting on the rifle: .22 caliber: 21-28gr Slugs sized .217 FX reports it recognizes that there are other comparable precision slug manufacturers and continues to develop slug liners to add to the series, along with additional caliber options.