This is not a question asking for information on how to tune one of my own Service rifles, but I'm interested in the experiences of others who have tried, whether successful or not, to tune a Service rifle to try and increase the power output.
Even though I own what is probably the only PCP Service rifle in the UK, converted by a very skilled engineer, John Walker of Hull, I'm not normally into delving into or modifying the internals of these rifles apart from lubricating and repairing where necessary.
Some time ago, I did read somewhere that someone had tried modifying a piston to take either an 'O' ring or synthetic head, I can't remember which, and also can't remember whether he was successful or not.