Early examples of pen guns were pinfired, but modern designs are rim or centerfire. They generally are of small caliber (e.g. Pen guns are zip gun-like firearms that resemble ink pens.
Homemade pen guns (Museum of the History of Donetsk militsiya). Larger zip guns, such as homemade shotguns called tumbera (Argentina), bakakuk (Malaysia), or sumpak (Philippines) are also made of improvised materials like nails, steel pipes, wooden pieces, bits of string, etc. The better designs use heavier pipes and spring loaded trigger mechanisms. 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. A rubber band powers the firing pin, which the shooter pulls back and releases to fire. 22 caliber rimfire cartridges, even very thin-walled tubing works as a barrel, strapped to a block of wood for a handle.
For small, low-pressure cartridges, like the common.
Zip guns are generally crude homemade firearms consisting of a barrel, breechblock and a firing mechanism.
