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