Things I liked:Nothing! I bought a WFH 22 cal that had this upgrade done to it by PA. These guns are supposed to shoot in the 900 fps range with 14.3 pellets. Mine shoots 750 fps way too slow. This is what my Trail NP shoots and it probably had the same piston installed intop the WFH. Not what it should be. Don't do it. What others should know:Find some of the new NPistons... by Moller and N Forcer have one of those put in.