Improvised firearm

An improvised firearm is a firearm manufactured other than by a firearms manufacturer or a gunsmith, and is typically constructed by adapting existing materials to the purpose. They range in quality from crude weapons that are as much a danger to the user as the target, to high-quality arms produced by cottage industries using salvaged and repurposed materials.

Improvised firearms are commonly used as tools by criminals and insurgents and are often associated with such groups; other uses include self-defense in lawless areas and hunting game in poor rural areas.

The essential part of any improvised firearm is the barrel and chamber. For small, low-pressure cartridges, like the common .22 caliber (5.5 mm) rimfire cartridges, even very thin-walled tubing will suffice. Author Harlan Ellison describes the zip guns used by gangs in 1950s New York City as being made from tubing used in coffee percolators or automobile radio antennas, strapped to a block of wood to serve as a handle. A rubber band provided the power for the firing pin, which is pulled back and released to fire. The use of such weak tubing results in a firearm that can be as dangerous to the shooter as the target; the poorly fitting smoothbore barrel provides little accuracy and is liable to burst upon firing.

More advanced improvised guns can make use of parts from other gun-like products. One example is the cap gun. A cap gun can be disassembled, and a barrel added, turning the toy gun into a real one; a firing pin can then be added to the hammer, to concentrate the force onto the primer of the cartridge. If the cap gun has a strong enough hammer spring, the existing trigger mechanism can be used as-is; otherwise, rubber bands may be added to increase the power of the hammer.

Air guns have also been modified to convert them to firearms. The Brocock Air Cartridge System, for example, uses a self-contained "cartridge" roughly the size of a .38 Special cartridge, which contains an air reservoir, valve, and a .22 caliber (5.5 mm) pellet. Examples of BACS airguns converted to firearms, either by drilling the barrel out to fire a .38 Special cartridge or by altering the cylinder to accept .22 caliber cartridges, have been used in a number of crimes. Blank-firing guns can also be converted by adding a barrel, although the low-quality alloys used for cheaper blank-firing guns may break with the pressures and stresses of a real bullet being fired.

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