I've changed mounts and that didn't solve it. I've added a rail, no change. I've changed scope and that didn't either. I've spoken to people with different end catches on the underlever and they have the same issues. My gun over the chrono even when demonstrating shift like in Italy was within 3fps of the shot when it wasn't demonstrating shift.
As with everyone else I see a vertical shift which seems to be temp related. Mine goes down in cold and up in heat, and really fast, like over 3-4 targets it will rise 20mm at 55 yds, and still group. At the end of Anston, despite almost clearing one side, down the other it was shifting 20mm low at 25yds. Strangely it affects the zenith rather than the far end... consequently i could get the long ones, but not the short ones.
It's been passed to a guru who's looked at the stock and it's inletting and fit, and so far he's reporting good things after fettling.
As much as i'm aware about position and it's effects, I can see this phenomenon in the same position just shooting it in as it changes. The vertical variation had me with 3 sets of numbers about 2-3 MOA apart from each other. In italy i saw a shift all through the range, so much so that I could dial 5yds less for targets. I know it wasn't the scope.
The only time i've seen a vertical shift like this with PCP's it's been either the gun shooting a different speed, or stock warping the action. So i'm hoping my guru's stock work has fixed it.
Incidentally, Mr Murphy says the only things that stopped his doing the same was going back to the original stock or using a Ginb... which is why he shot a right handed tx stock despite being left handed...
But the good news is that now more are using them more frequently over courses which test the overall package, the problem is becoming seen more and more people are working on it.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep