Lee machines their mold blocks from aluminum, ensuring rust resistance and long-lasting durability. Aluminum molds heat up and cool down faster than iron or steel molds, allowing bullet casters to produce quality bullets with just a few casts. Additionally, aluminum blocks are one-third the weight of iron or steel mold blocks, reducing fatigue during extended casting sessions. To guarantee the best possible bullets, Lee CNC machines each mold block half for precise roundness and size control. The listed weights are based on Lee's suggested alloy, though actual weight may vary depending on the alloy mixture used.