Shimming the stock will not change POI if you’re AIMING a turkey gun like a rifle. That only applies for wingshooting. It’s like saying adjust your stock instead of your scope to zero your rifle. Barrels can be trued….just not sure who does it anymore. Sights/optic and adjusting POA vs poi from there….sounds like what you might need. Kicks chokes were always my best patterning with turkey loads in 12ga Remchoke guns. JEBS, Indian Creek, Trulock….any should get you there. Im not much of a Carlson’s fan, but that’s a company attitude thing…not a product thing.