If you cast your own bullets, then this tool allows the reloader to bring the bullet down to size and apply lubrication. Lyman improved sizing dies now have 90° hole spacing for easier bullet lubrication, even with today's hard lubricants. Lyman sizing dies also feature a tapered mouth and hardened interior insuring alignment for perfect cylindrical shape. Interior dimensions correspond to suggested diameters for all popular rifle and pistol calibers. Refer to the chart below for proper size. (These are interchangeable with RCBS)