BSA Ultra De Tune

BSA Ultra purchased new from a Gun Dealer. Using H&N Barracuda Match Pellets, the air rifles muzzle power output was about 15 ft/lb. I was extremely reluctant to return it to the shop incase they charged me for the work or worse still, kept it until I had an FAC. After some experimenting, I found this method to be effective. I don't know if this is the correct way of doing it, but it worked for me with no adverse affects to the gun consistency (if anything, the FPS margins were tighter). This procedure was carried out while the rifle was fully pressurised. If there is anyone who can advise me on a better/more effective way, please let me know.