By reducing piston weight you would possibly reduce power, So to increase spring length to gain power lost and to possibly gain more recoil, Myself i would aim to set gun if 177 cal to about 10.5 , If you've recently bought the gun I would get a good few months of shooting out of it first before I started going to far with it, My lgu had a kit fitted already to it , That was 177 cal and was shooting at 10.5, The chap who bought it off me phoned me recently to say how smooth and lovely it shot compared to his tx which has had a lot of money on it with regards to tuning,