1) Verify tightness of sight system screws, preferably mount a scope of known function.
2) Try different bullet/sabot combinations.
3) New powder.
4) New breech plug -- I've never needed one but some people claim the holes widen enough to affect accuracy
5) Torque of action screws. My omega was volatile before I intalled pillars and the accuracy changed depending how I tightened the action screws.
6) Verify breech closing mechanism is tight.

Go through the list in the order of least cost/greatest convenience to you!!