 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.Pen guns are zip gun-like firearms that resemble ink pens.They generally are of small caliber (e.g., .22 LR, .25 ACP, .32 ACP, .38-caliber, etc.)