Lee machines their mold blocks from durable aluminum, which ensures they are rust-resistant and perform reliably over time. Aluminum molds heat up and cool down faster than traditional iron or steel molds, allowing bullet casters to produce quality bullets in just a few casts. Additionally, aluminum blocks are one-third the weight of iron or steel, significantly reducing fatigue during long casting sessions. To guarantee the highest precision, mold block halves are CNC-machined, ensuring exceptional roundness and size control for every bullet. The provided weights are based on Lee's suggested alloy, though actual weight may vary depending on the alloy mixture used.