Lee machines their mold blocks from aluminum, ensuring rust resistance and long-lasting performance. Aluminum molds heat up and cool down more quickly than iron or steel, allowing for high-quality bullets to be produced after just a few casts. In addition, aluminum blocks are one-third the weight of iron or steel molds, reducing fatigue for bullet casters during prolonged casting sessions. To guarantee the best possible bullets, Lee CNC machines each mold block half, ensuring precise roundness and tight size control. The weights provided are based on Lee's suggested alloy, with actual weight varying depending on the specific alloy mixture used.