 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.Zip guns are generally crude homemade firearms consisting of a barrel, breechblock and a firing mechanism.For small, low-pressure cartridges, like the common .22 caliber rimfire cartridges, even very thin-walled tubing works as a barrel, strapped to a block of wood for a handle.