RCBS Full-Length die sets are machined from RCBS's proprietary die steel to exacting tolerances then undergo a meticulous finishing process to give the hand-loader the best dies on the market. Each Full-Length set includes a Full-Length sizing die and Bullet Seating Die. These two die-sets are intended for reloading bottleneck cases, and consist of a Full-Length Sizer Die with an Expander-Decapping Unit, and a Seater Die with Bullet Seater Plug. The Full-Length Sizer Die brings the case to SAAMI minimum cartridge dimensions. This die sizes the outside of the case, de-primes, and expands the neck to accept the bullet. The die has vents to prevent case damage caused by trapped air and excessive lubricant. Headspace is held to minimum tolerances to avoid changing the case body length during full-length sizing. The included Seater Die has a built-in roll crimper to secure the bullet at the same time as it's seated.