Tuning a Webley Service rifle.

[Troubledshooter]

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.

[Shed tuner]

I replaced the piston rings with a regular rubber o-ring - no modifications necesary - and it added a little power and made it a little less slammy, but nothing earth shattering. Then again, it took 5 minutes and cost about 10p

[Binners]

I find it hard to believe that Webley designed and produced such a well engineered rifle and fitted poxy bronze split piston rings????

I think a certain J M on here has a rifle that has a piston head mod...

[Shed tuner]

I find it hard to believe that Webley designed and produced such a well engineered rifle and fitted poxy bronze split piston rings????

I think a certain J M on here has a rifle that has a piston head mod...

Well engineered but in many ways not well designed... Too much lost volume. I like them, but it's always the bsa underlever I pick up if I want a vintage plink that will actually involve hitting the target