The Lyman 1-Cavity 20 Gauge Shotshell Foster Slug Bullet Mould is made from solid leaded-steel and machined to an exact and smooth super fine finish. The mould is then heat treated (that is why it is blue in color) and feature hardened steel alignment pins to provide many years of bullet casting service. Sprue plate is 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 mould. This mould cast perfect hollow base Foster-style slugs which do not require rifling. Slug mould is 1-cavity mould that is cut into the larger 2-cavity mould block.