How many firings were on the brass that shot on the original magic load 3 shot group? Even if you anneal, if you have some virgin brass you can try the magic load with to verify your annealing process.
You didn't state it, but are all components from the same lot? Specifically your powder?
The above two would be my first bets.
Do you have access to a concentricity tool? In my limited experience, this will have a direct effect on the potential precision of any ammunition, although your group shape suggests either velocity/pressure variation, or the shooter. Since your user name suggests association with the USMC...we all know that isn't likely
Go try some virgin brass!