RCBS full length 2-Die Sets are for bottleneck type and consist of a Full-Length Sizer Die with Expander-Decapping Unit and a Seater Die with Bullet Seater Plug. The Full-Length Sizer Die brings the case to SAAMI minimum cartridge dimensions. It 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 for 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.