I bought a AA S400 FAC Xtra a couple of years back from one of the forum members (cant remember who though) but any way here is my story.....
1. the rifle came installed with a LW 5mm Barrel.
note that all tests were done with 13.7gr JSB Pellets and 190Bar fill pressure
2. Standard rifle: 60 shots on one fill from 190 bar to 100bar; High of 1016ft/s and a Low of 869ft/s (Blue Line on Chart)
3. Louis from Airgun warehouse installed a Robert Lane Anti Bounce Hammer Kit. 110 Shots from 190bar to 100bar, High of 952ft/s and Low of 807ft/s, but had a nice 30 shots sweetspot between 150bar and 130bar with a high of 952fts and a low of 935ft/s.(Green Line on Chart).
4. Then after 2 months Louis fit a Robert Lane Regulator as well and this was the result: 60 Shots with a high of 930ft/s and a low of 913ft/s. (Red Line on Chart)
The end Result = supper accurate and efficient air Rifle
Thank you Louis from Airgun Warehouse.