Savage went to the large shank size shortly after they started offering the WSM and RUM's in their rifles in the early 2000's. The larger diameter of those cases results in a thinner barrel wall in the chamber area which makes it more prone to swelling given the higher 65kpsi pressure rating of these rounds. The larger shank diameter puts more material back in the barrel shank to make it stronger and more resistant to swelling. Several have built WSM's on standard shank actions, but if Savage saw fit to up the shank size and tool up/inventory another size barrel nut and recoil lug you can rest assured there was good reason for it.