Gunmetal, also known as red brass in the United States, is a type of bronze – an alloy of copper, tin and zinc. Proportions vary by source, but 88% copper, 8-10% tin and 2-4% zinc is an approximation. Originally used chiefly for making guns, it was eventually superseded in this department by steel. Gunmetal, which casts and machines well and is resistant to corrosion from steam and salt water, is used to make steam and hydraulic castings, valves, gears, statues and various small objects, such as 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.
• 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.
• U.S. Government bronze specification H is composed of 83% copper, 14% tin, 3% zin and 0.8% phosphorus.
• Red brass is used to produce pipes, valves and plumbing fixtures and is considered to offer a good mixture of corrosion resistance, strength and ease of casting. It typically contains 85% copper, 5% tin, 5% lead and 5% zinc.
• Copper Alloy C23000, which is also known as red brass, contains 84-86% copper, 0.05% each iron and lead, with the balance being zinc.
Gunmetal can also mean steel treated to simulate gunmetal bronze. Bushings made of this metal are used in machinery.