A range of different grades of steel are used in the manufacture of a single firearm. Chromium-molybdenum steel is the basic material for the modern firearms industry. It possesses good tensile strength, resists wear, and has good machining properties. Most .22" rimfire caliber guns, shotguns, and low pressure centerfire barrels are made from carbon steels. High-pressure centerfire barrels for sporting use are normally made from chromium-molybdenum-vanadium steel.
The grades of steel used for the many different component parts involved in a single firearm can vary from manufacturer to manufacturer, but they all contain some of the following elements in order to achieve the desired metallic properties: chromium, copper, manganese, molybdenum, nickel, phosphorus, silicon, tungsten, and vanadium. Aluminum alloys are also used in the manufacture of firearms (and telescopic sights) and contain some of the following elements: chromium, copper, iron, magnesium, manganese, nickel, silicon, and zinc.100 Springs used in firearms may contain beryllium and copper and some parts such as sights may be attached by brazing or silver soldering. Stainless steel is being increasingly used for the manufacture of firearms. Stainless steels range from 12% to 24% chromium with other additives such as molybdenum and nickel.
The trend is toward lightweight handguns and rifles and increasing use is being made of polymers (plastics) for the manufacture of parts such as stocks, grips, frames, magazines, and so forth. Polymers have considerable advantages. They are lightweight, durable, inexpensive, noncorrosive, and easily molded to any required shape, thus eliminating the need for expensive tooling to machine a firearm to the desired shape.
A wide range of woods are used in the manufacture of solid wooden stocks for rifles and shotguns; one of the most popular is walnut. Laminated wooden stocks are also used, and consist of thin strips of wood that are impregnated with epoxy and compressed into a solid block.
Synthetic stocks are gradually replacing the traditional wooden stock due to their cheapness, ease of manufacture, lighter weight, and wear ability, and are claimed to be more stable and easier to maintain than wooden stocks. Materials such as nylon, polyurethane, fiberglass, Kevlar reinforced with fiberglass or carbon fiber, or thermoplastic resin reinforced with glass and ceramics may be used. The stocks may be hollow, or have a hollow filled with foam or a solid. Such stocks may be surface-treated with a coating such as polyurethane.
Grips may be made of wood, plastic, laminated phenolic resin, or rubber, and rubber is also used for recoil pads. Customized or ornamental firearms may have grips made from ivory; mother of pearl, or buffalo horns, and the firearm may have elaborate engraving some of which is inlaid with gold or silver. Such firearms are unlikely to be used in crime.
Homemade firearms are encountered in crime, and materials used in their construction vary markedly. Some of them are finished with household paint, and flakes of paint transferred to the criminal's clothing can be of considerable evidential value. The grips of some homemade firearms are metal and are sometimes covered with plastic adhesive tape. Plastic adhesive tape may also be used to tape magazines together for use with commercially manufactured firearms, so that the firearm can be reloaded rapidly. Fingerprints may be obtained from the tape and a comparison of tape ends with the ends of tape recovered from a suspect's home or workplace can yield very strong evidence if a physical match is obtained. The same applies to tool mark impressions from machine tools at a suspect's home or workplace.
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