Could be lots of things....

Muzzles crown could be damaged either from when it was originally done at the factory or from cleaning etc....

Chamber issues. What kind of run out does your fired brass have.

Does the barrel copper foul bad? If it’s copper fouling bad then you can have a fouling issue. Heavy build up on top of the lands is a accuracy killer. From a good clean bore if you have fouling issues the accuracy will usually go sour in about 15-20 rounds.

Get a good stock and bed it or a chassis stock. Sorry but factory stocks and fit is a issue. Sometimes you get lucky with the fit and sometimes you don’t.

Later, Frank
Bartlein Barrels