The RCBS 12201 is a dual-die set designed specifically for reloading bottleneck cases. Included in this set are a Full-Length Sizer Die, equipped with an Expander-Decapping Unit, and a Seater Die which features a Bullet Seater Plug. The Full-Length Sizer Die is crafted to reset the case to the Saami minimum cartridge dimensions. This die efficiently sizes the case exterior, de-primes, and widens the neck to accommodate the bullet insertion. It features vents devised to deter case damage that could be induced by trapped air or excessive lubricant. The Full-Length Sizer Die maintains headspace within minimal tolerances to avoid altering the case body length during the full length sizing process. The provided Seater Die incorporates a built-in roll crimper, designed to ensure the bullet is securely seated and crimped simultaneously.