Although you can neck size with the full length sizing die it's not recommended. When the case is fired it walls expand. Although it can't be seen with the naked eye, the case is buldged. What happens when you partcally size the case using the full length sizing die, the sizing die removes the buldge pushing the shoulder forward. Because the full length sizing die is backed out it fails to push the shoulder back creating a long shoulder to base case.
Clifford L. Hughes