RCBS Neck Sizer Die 308 Norma MagnumRCBS Neck Sizer Dies size only the neck of case (not the shoulder or body) just enough to snugly hold the bullet which leads to increase case life and accuracy. Die Type: Neck Sizer Die (with expander decapping unit) Accessories: Plastic Storage Case Notes: Neck Sizer Dies size only the neck of the case (NOT the shoulder or body) just enough to snugly hold the bullet for extended case life and accuracy