Consider the shooter - good stable table or prone, little hopping of the muzzle during firing, maybe sandbags or a pedestal rest with rear bag if using a bipod. Is the shooter usually grouping smaller with other rifles?
For the Rifle, open up the forend so there LOTS of room around the barrel. If you can squeeze the stock to touch the barrel, make more room. Maybe the scope?
For the ammo, try another type. Not all factory ammo is going to like all barrels. Reload
Start here and tweak as you get more results.
Jerry