Sorry for your troubles Gb. I'd start around 125 bar on the reg. Another stab at it....possible pellet clipping? You could try a string with the shroud off and see what happens. Nothing to lose at this point. A cracked air stripper or bad oring up there may cause just enough mis alignment to make it clip. One other thing, and probably not enough to cause your wide velocity swings. My 25 would lead up real bad after only a couple hundred pellets down the barrel. And nothing but a bronze brush would clean the lead out. Hope you get it figured out.