So having had my chrono arrive today I decided to test it before replacing a few bits.
First chrono was around 230-240 FPS, and seeing as the rif is shooting a lot better than when I first got it im guessing it must have been sub 150 to begin with.
Anyway, having double checked shims, replaced nozzle, piston, bucking and nub a quick re-lube, it is now consistent between 308-310 FPS. The air seal on the cylinder isn’t perfect and a bit of ptfe has been put in for now. But I think once I replace the cylinder head and possibly put a tight bore barrel in I could get it upto 330. However I’m happy where it is now and shall leave it be until I’ve used it a few times.