Lyman 1-Cavity Bullet Molds are made from solid leaded-steel and machined to an exact and smooth super fine finish. The molds are then heat treated (that is why they are blue in color) and feature hardened steel alignment pins to provide many years of bullet casting service. Sprue plates are made from solid steel, ground flat and held tightly in place with tempered steel spring washers and screws. In addition, break-in is often half the time required for iron molds. These molds cast perfect hollow base Foster-style slugs which do not require rifling. Slug molds are 1-cavity molds that are cut into the larger 2-cavity mold block. Specifications: - Mold Caliber: 12 Gauge- Diameter: 0. 681"- Bullet Weight: 525 Grains- Bullet Style: Slug- Material: Steel- Handle Included: No- Gas Check: No- Capacity: 1