If you’re going with a stainless steel barrel, I suggest at least a #5. That way you have enough metal to safely add muzzle threads if you want them or may want them added later. Other than that, it’s your preference. Since you mentioned it’s a hunting rifle, I would keep it smaller (outside diameter) to save weight. Otherwise, carbon fiber would be a great choice. You may have to modify your stock to accept the larger diameter barrel though. That depends on your stock.What barrel contour would you recommend for a hunting rifle for a Tikka prefit?