Slug shooting requires higher pressures to move the additional weight and bearing surface that slugs have. In addition, with the use of longer barrels, speed can be increased upon firing, if the valve can remain open longer. Both can be achieved with a first ever in the airgun world: the FX Impact Tungsten Hammer Weight.
Tungsten is a material that is 1.7x denser than steel (used for the standard FX hammers). This extra weight hits the valve with more power which allows the valve to open even at higher regulated pressures and stay open longer before closing.