The RCBS Small Base Die Set - A must for the progressive reloader. It features a Small Base sizing die anda new Taper Crimp seating die. This combination makes reloading easierfor AR-style or semi-auto shooters. The Small Base sizer guarantees thatthe cartridge will rechamber. The Taper Crimp Seater is more forgiving whenvarious case lengths are loaded at the same time. Case neck crimp bulgesand buckled shoulders are virtually eliminated when Taper crimping is usedwith cannelured bullets.