RCBS is the industry leader in reloading straight-walled cartridges for rifles and pistols. The 3-Die Roll Crimp Set includes a hardened steel Sizer Die, Expander Die, and Roll Crimp Die. Lubrication is required when using the Sizer Die. The expander Die expands the case to the proper diameter to accept the bullet. The Seat Die seats the bullet in the cartridge case and 'roll' crimps the case to eliminate movement during recoil. All RCBS dies are machined to exacting tolerances, hardened and finished to the highest standards in the industry.