Hello Danny,

Thanks for the suggestions. I've already installed the GMac extended brass breech (I wanted to keep the stock sight without modding it...) with the extended probe. I understand they don't do a hollow probe for the .177 version - what's the point anyway? I've also added a transfer port top seal, I'm guessing that has more or less the same effect as replacing the metal port with a vinyl one. Also deburred the transfer port.
I have the impression that this already increased the power - I'm now shooting through board that resisted previously.
The flat top piston kit from gmac will be next.

In fact, I was a bit concerned that there might be some security valve somewhere that would continue to limit the max output - any ideas if that's likely or rather not?