RE: Sighting in
You need to start over with a clean gun for starters. As someone mentioned you need a good copper solvent cleaner and the barrel needs to be broke in, but barrel break in would not cause a creep.
NOTE:after cleaning a gas operated auto it is especially important to wear safety glasses when shooting next. Cleaner can get in gas chamber.
Go back to the range, shoot and take exacting notes of what happens. Shoot three or four three shot groups, forget the first one.