Lee machines their mold blocks from aluminum, offering rust resistance and enhanced durability. Aluminum molds have the advantage of heating up and cooling down faster than their iron or steel counterparts, enabling bullet casters to produce quality bullets after just a few casts. Additionally, aluminum blocks weigh one-third as much as iron or steel molds, reducing fatigue during extended casting sessions. To ensure top-notch performance, the mold block halves are CNC-machined for precise roundness and size control. The listed weights are based on Lee's recommended alloy, though actual weight may vary depending on the alloy mixture used.