I've been down the hw moving zero road...when it happened to me I chrono'd the gun and every thing was fine on the chrono??? But my zero was 3inch high all through the ranges, I personally think the problem is down to the crappy bit of bent metal that holds the front stock screws regardless if you actually use the screws or not, It's still loose? Be interested to know if some one who is experiencing the same thing could have that part changed for a solid non moving part and see if it works (same as the air arms one)...any engineers fancy it?
EV2mk4-Nikko nato mk1
Pro-Target-Nikko nato mk3