The punch and base de-caps the primer from the case while providing a stable base. Bases are case hardened for wear resistance. Available for most calibers. Punch Out Primers on your Cases in a Separate Operation Works Great for Military Primers Many Precision Shooters Prefer to Punch Primers Out Prior to Sizing To Determine the Correct Size Simply Measure your Case Head Diameter. For example a 223 Remington head measures .375" so you would need a .380 Base Made in the U.S.A