The Lee Original Minie Ball Bullet Mould - Single Cavity .575 diameter and 500 grain is ideal for people who enjoy reloading. The blocks are constructed of rust-resistant aluminum, capable of heating up and cooling down more quickly than moulds made from steel or iron. Because of this, high-quality bullets are produced within minutes.Another benefit of the aluminum construction is that this mould is much lighter than iron or steel. As a result, there is less fatigue on the bullet caster during long or repeated casting sessions. For perfect roundness and size control, the block halves are CNC machined.