From Sharp Shooter Supply - The Savage Specialists
Tech Updates at the bottom of the Home Page on the left.
In 2002 Savage offered rifles in the Winchester Short Magnum (WSM) and Remington Ultra Magnum (RUM) calibers. When these were finally in the catalog, there was a change made to the barrel shank diameter. Standard barrel shank diameter on standard calibers are 1.055" x 20tpi. On the new WSM, RUM, and SAUM calibers it is 1.120" x 20tpi. The barrel nut is also bigger in internal size, but is the same outer diameter and our barrel nut wrench will still fit. Savage also used this size of shank on the first version of the Model 10ML muzzleloader.
However, there were a few WSM and RUM rifles made on the standard barrel shank in the first production run. The best way to tell is to measure the barrel shank right against the nut. The larger barrel shank will have a step down approximately 1/8" ahead of the barrel nut. If your rifle has a serial number with a "G" prefix, it is most probable it will have the larger shank."
Info and picture taken directly from the site listed above.