Gunmetal
Gunmetal, also known as red brass in the United States, is a type of bronze – an alloy of copper (85%), tin (5%), and zinc (5%), and lead (5%). Originally used chiefly for making guns, gunmetal was eventually superseded by steel. Gunmetal casts and machines well, is resistant to corrosion from steam and salt water, and is used to make steam and hydraulic castings, valves, and gears, and also statues and various small objects, e.g. buttons. It has a tensile strength of 221 to 310 MPa, a specific gravity of 8.7, a density 8,719 kg/m3, and a Brinell hardness of 65 to 74.
Variants
Gunmetal ingot is a related alloy where the zinc is replaced by 2% lead; this makes the alloy easier to cast, but it has less strength.
Modified gunmetal contains lead in addition to the zinc; it is typically composed of 86% copper, 9.5% tin, 2.5% lead, and 2% zinc. It is used for gears and bearings.
U.S. Government bronze specification G C90500 is composed of 88% copper, 10% tin, and 2% zinc.
G bronze (or Copper Alloy No. C90300) contains 88% copper, 8% tin, and 4% zinc.