An improvised firearm is a firearm manufactured by someone who is not a regular maker of firearms, such as a firearms manufacturer or a gunsmith, and are typically constructed by adapting existing materials to the purpose. Called by many names, these improvised firearms range 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 more commonly found where legal and commercially produced firearms are unaffordable or strictly controlled. If commercial ammunition is obtainable, then improvised arms will generally be built to fit that ammunition. If commercial ammunition is not available, then muzzle loading black powder designs can still be produced.
Most countries have controls in place that regulate production, sales, and possession of firearms and ammunition (see Gun politics for regional information). This means improvised firearms are for the most part illegally produced, which makes their possession and use criminal as well. Improvised firearms are commonly used as tools by criminals and insurgents. These improvised firearms are still in use by both criminals and rebels in the Philippines.
Not all uses of improvised firearms are used to facilitate violent crime or revolt, however. In areas where crime is rampant, these firearms may be used for self defense by lawful citizens, or they may be used in poor rural areas for poaching game for food or profit.
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 provides 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 more dangerous to the shooter than 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, or BACS, 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. This resulted in legislation that classified the BACS air guns as firearms, which effectively banned them in the United Kingdom in 2004. Blank firing guns can also be converted by adding a barrel.
Some more complex improvised firearms are not only well built, but also use mimicry as camouflage, taking the appearance of other items. Improvised firearms in the form of flashlights, cellular telephones, pens, and large bolts, have all been seized by law enforcement officials. Most of these are .22 caliber rimfires, but flashlight guns have been found ranging from small models firing .22 Long Rifle to larger ones chambered for .410 bore shotgun shells.
While most improvised firearms are single shot, multiple shot version are also encountered. The simplest multi-shot zip guns are derringer-like, and consist of a number of single shot zip guns attached together. In late 2000, European police encountered a four shot .22 LR zip gun disguised as a cellphone, where different keys on the keypad fire different barrels. Because of this discovery, cellphones are now x-rayed by airport screeners worldwide. They are believed to be manufactured in Croatia, and were still being found in Europe as late as 2004, according to a report by Time magazine.
The British Sten, while it was an official military firearm, was developed specifically to be produced by improvised workshops. When the British Expeditionary Force withdrew from France in the Dunkirk evacuation of 1940, large numbers of arms were abandoned, leaving the British military under-armed. Two Britons, Sheppard and Turpin (the "S" and "T" in "Sten") designed and built a prototype submachine gun in 30 days' time, to be used to re-arm the British soldiers as quickly as possible. Intended to resist an anticipated German invasion, the gun was designed to fire captured Axis 9x19mm ammunition, and was simple to construct, with a minimum of precision parts. Production was implemented as a decentralized assembly line, with production operations spread out to over 300 improvised production facilities throughout Britain. An additional advantage of the deliberately primitive construction of the Sten was a great reduction in production costs. The initial production cost of the Sten was approximately US$12 per unit, and quickly dropped to US$8 with improvements in production techniques, a fraction of the approximately US$120 required for an American Thompson or the German "Schmeisser" MP40 submachine guns.
In cases where some firearms are available, they can be improvised into different types. One such improvised, repurposed firearm is described by Che Guevara in his book Guerrilla Warfare. Called the "M-16", it consists of a 16 gauge sawed-off shotgun provided with a bipod to hold the barrel at a 45 degree angle. This was loaded with a blank cartridge formed by removing the shot from a standard shotshell, followed by a wooden rod with a Molotov cocktail attached to the front. This formed an improvised mortar capable of firing the incendiary device accurately out to a range of 100 meters.
Flare guns have also been converted to firearms. This may be accomplished by replacing the (often plastic) barrel of the flare gun with a metal pipe strong enough to chamber a shotgun shell, or by inserting a smaller bore barrel into the existing barrel (such as with a caliber conversion sleeve) to chamber a firearm cartridge, such as a .22 Long Rifle.
Improvised firearms are typically illegal, and are commonly associated with gangs, where they may be used to facilitate violent crime, such as homicide. In other cases, they may be used for other criminal activities not directly related to violent crime, such as illegal hunting of game.
Improvised firearms are most commonly encountered in poverty stricken regions with restrictive gun control laws. While popular in the United States in the 1950s, the "zip gun" has become less common due to the greater ease of obtaining firearms on the black market. In India, use of improvised country-made pistols is widespread, especially in the regions of Bihar and Purvanchal. The manufacture of these weapons has become a cottage industry and the components are often manufactured from scrap material, such as gun barrels fashioned from truck steering wheels. In areas like South Africa, improvised firearms are more common. In a study of Zululand District Municipality, South Africa, it was found that most improvised firearms were crude, 12 gauge shotguns, with a simple pull and release firing mechanism; like the .22 rimfire cartridges, shotgun shells also operate at low pressures, making them more suited for use in weak, improvised barrels. Even in the absence of ammunition, home-made powder can be used; such firearms were the subject of a crackdown in the People's Republic of China in 2008.
Improvised firearms are not solely the province of the criminal element, however; they are also used by insurgents. During the Japanese occupation of the Philippines during World War II, the paliuntod, a type of improvised shotgun, was commonly used by guerillas and American soldiers who remained behind after Douglas MacAurthur's withdrawal. Made of two pieces of pipe that fit snugly together, the paliuntod was a simple, single shot open bolt design. The shell was placed in the breech of the barrel, which was then fitted into the larger diameter receiver. The receiver was capped at the breach end, and had a fixed firing pin placed to strike the primer of the shell. When the barrel was pulled sharply to the rear, the firing pin would strike the primer and fire the gun. These improvised firearms are still in use by both criminals and rebels in the Philippines.
Danao City, in the Cebu province of the Philippines, has been making improvised firearms so long that the makers have become legitimate, and are manufacturing firearms for sale. The Danao City makers manufacture .38 and .45 caliber revolvers, and semi automatic copies of the Ingram and KG submachine guns.