So you're in the UK and you have FAC, but you will need to put that particular rifle on your ticket in order to legally modify for FAC power and once done cannot be reversed, if you can prove you have FAC I will give you the info needed, otherwise I would be breaking the law as it just sounds like your trying to up the power on a restricted rifle to me, and nobody on a UK forum will give you that info.
The 818 fps you are showing is only 11.2ftlb with the 7.56 grain pellet you're using and not FAC power?
