Huma have made a Pin Probe model for the FX Impact.
In combination with there Dual Hole, V2 high flow transfer port and power tuning hammer spring you will gain the ultimate performance out of your FX Impact specially when you shoot slugs.
Although this probe is specially developed for slugs we get a lot feedback from guys using it for pellets too.
Any modification done to the airflow of your rifle, will affect the entire setup and performance, you might need to re-adjust the settings of your rifle again to get the best possible performance.
Available in .22, .25 and .30