A must for the progressive reloader. The RCBS AR Series Die Set features a Small Base sizing die and a Taper Crimp seating die. This combination makes reloading easier for AR-style or semi-auto shooters. The Small Base sizer guarantees that the cartridge will rechamber. The Taper Crimp Seater is more forgiving when various case lengths are loaded at the same time. Case neck crimp bulges and buckled shoulders are virtually eliminated when Taper crimping is used with cannelured bullets.