Lee machines their mold blocks from aluminum, offering rust resistance and ensuring long-lasting performance. Aluminum molds heat up and cool down more quickly than iron or steel molds, allowing bullet casters to produce quality bullets after only a few casts. In addition, aluminum blocks are one-third the weight of iron or steel molds, reducing fatigue during extended casting sessions. To guarantee the best possible bullets, mold block halves are CNC-machined to ensure unmatched roundness and precise size control. The weights provided are based on Lee's suggested alloy, but actual weight may vary depending on the alloy mixture used.