Clean it good.
I was intitially elated with my 223 and the WW varmit amo. Decided to get another scope for it everything was working so good.
Put on the scope and started sighting in and it just didn't seem right. Took it apart. Did the trigger job thing. Stuff still just kept getting worse.
Finally just sat and thought about it a minute and realised I'd probably put 30 or 40 rounds through it with sighting in two scopes, trigger job tests, and just fooling around.
Did the through cleaning and even polished the chamber. Did the whole flitz thing on the barrel and deep cleaned again. Rechecked and tightened all screws and it's probably shooting better than ever it seems.