The RCBS two-die set is for bottleneck cases to be fired in bolt-action rifles only - specifically, cases fired out of a specific rifle and neck-sized to go back into the same rifle. The set consists of a Neck Sizer Die with an Expander-Decapping Unit, and a Seater Die with Bullet Seater Plug. The Neck Sizer Die resizes the neck only (it doesn?t touch the shoulder or body) and de-primes. The included Seater Die has a built-in roll crimper to secure the bullet at the same time it?s seated.