As a general rule, and this goes for .340 Weatherbys and smaller, the length of the barrel determines the contour diameter. For example, a Weatherby Mark V in .300 Weatherby with a 26" barrel will have a .600 muzzle diameter. The same rifle with a 24" barrel will have a .560 muzzle diameter. Weatherby calls a 24" barrel as a #1 contour. The 26" barrel with a muzzle diameter of .600 will be a #2 contour. I have seen #3 contour barrels, but they are pretty rare. Hope this information helps.