As for the question as to which manufacturers best regulate their barrels, I think the answer would be those who build guns for the most demanding levels of comptetion AND build essentially the same gun for field use. I expect that an Olympic class clays or high stakes flyer shooter with reputation and money riding on performance is not going to accept anything less than outstanding regulation.

Perazzi, Kreighoff, and Fabri come to mind. They are used by top-level competition shooters and their field and target guns differ only in minor details. I am sure there are others.