The RCBS 20515 refers to the 3-Die Carbide Sets from RCBS, which are optimal for straight-wall rifle and pistol cases. The highly efficient Carbide Sizer Die not only sizes the case but also de-primes it. The utilization of a carbide sizer ring gets rid of the need for lubrication.Alongside this, the Expander Die functions to enlarge the case to the appropriate diameter to accommodate the bullet, and also inflicts a case mouth flare/bell for bullet feeding. Lastly, the Seater Die works to seat the bullet and facilitate roll crimps.