The 3-Die Roll Crimp Set is for loading straight-wall cartridges. Its steel Sizer Die sizes the case and de-primes. Note: Cases must be lubricated. The Expander Die expands the case to the proper diameter to accept the bullet, and it imparts case mouth flare/bell for bullet feeding. The Seater Die seats the bullet and roll crimps. RCBS: PRECISIONEERED RELOADING. RCBS has dedicated itself to the craft of handloading ammunition since it was founded in 1943. RCBS is the leading manufacturer of reloading equipment for rifles and pistols. Reloading is an exact process with tight tolerances. It requires precision and skill to be done correctly. Thats why RCBS makes state-of-the-art products all are backed by RCBSs industry-leading reputation.