Both the long and the short scope bases may be used on the short action. The difference between these two base types: On the short scope base set the "front" mount scope ring is positioned at the front of the base. This base ring assembly would be ideal for use with rifle scopes that have a very long overall length and you want to get as much support as possible. It would also be a good choice if you "crawl" the stock and need to move the scope further forward to get correct eye relief. On the long scope mount "front" ring and base assembly, the scope ring is positioned at the rear of the base. This is ideal for if you need the ability to mount the scope further to the rear to achieve correct eye relief, or if you are mounting a "compact" scope with a very short main tube. Typically, we recommend the long assembly on the WSM to ensure that the scope is located as far forward as possible to prevent "scope eye"; but obviously, there are many personal factors that could affect this.