Brass
The cartridge case, bullet, bullet coating, and metal jacket also contain specific elements that can be detected. Virtually all cartridge cases are made of brass (70% copper and 30% zinc). A few have a nickel coating. Primer cases are of similar composition (Cu-Zn). Bullet cores are most often lead and antimony, with a very few having a ferrous alloy core. Bullet jackets are usually brass (90% copper with 10% zinc), but some are a ferrous alloy and some are aluminum. Some bullet coatings may also contain nickel. (Ravreby, 1982).
Modern gunpowder, or "smokeless" powder, can contain up to 23 organic compounds (FBI study). Nitrocellulose is virtually always present, along with other compounds containing nitrate or nitrogen. One of these compounds, diphenylamine (used as a stabilizer in the powder), can be detected using reagents containing sulfuric acid. (Maloney et al, 1982) Modern gunpowders are also described as "single-base" when the basic ingredient is nitrocellulose and as "double-base" when there is additionally 1 to 40% nitroglycerine added. Hardy and Chera (1979) describe a method to differentiate them using a mass spectrometer.
In the physical examination of the scene or body for evidence of gunshot residue, it must be remembered that lead residues may mimic gunshot residue. Lead residues may be found up to 30 feet from the muzzle, and are always present on the opposite side of a penetrated target. Such a situation has been reported when an intermediate target (glass) was present. (Messler and Armstrong, 1978)
Though the amount of residue deposited tends to decrease with increasing range of fire, the actual deposits can be highly variable for ranges up to 20 cm.(Brown, Cauchi, et al, 1999)