This article should help.
Savage Barrel Shank Sizes
Rate this article
Published on 01-23-2012 12:06 PM Number of Views: 1445 2 Comments
In 2002 Savage began offering 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 the shank diameter 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 WSM or RUM rifle has a serial number with a "G" prefix, it is most probable it will have the larger shank.
NOTE: The new 12LRPV's and Target Series rifles with an extra heavy target barrel uses the large shank size. Due to the extra heavy contour there is no "step" in the barrel as shown in the picture above.
The quickest way to determine what size the barrel shank is on your rifle is to measure the length of your barrel nut. Standard shank nuts are 7/8" (0.875") in length, whereas large shank nuts are 5/8" (0.625") in length.
Information provided by Fred Moreo