A very well-disguised 22 firing device was recovered from an outlaw biker during a dmg-related arrest. Built into a tire gauge, this single shot weapon shows excellent machining and design. It fired safely and accurately at short ranges. (Courtesy of FBO The .22-caliber round is generally very safe to the improvised gun firer. Even in weapons where a breechface is nonexistent the thickness of the cartridge base is such that it can withstand the firing pressure virtually unsupported. Cases often bulge and sometimes burst. Yet, even when they do, the .22 cases simply peel back rather than fragment, presenting little danger to the shooter. The barrel for a .22 zip gun usually is a section of car antenna flared to fit and then taped to a wooden grip. Other .22-caliber barrel expedients include grease-nipple rods, threaded lamp-cord rod, and bar stock drilled with a 15/64 bit. The firing pin is often a nail or a sharpened small bolt driven by a spring or rubber band . Accuracy tests are meaningless, as these .22 weapons are for point-blank distances only. Penetration varies proportionately to the amount of breech support at the base of the cartridge. With well-made zip guns the results are the same as those obtainable from pistols; most are not well-made. The user-friendly, target-harming tendency of these projectiles to keyhole often makes formal penetration testing academic. However, penetration of at least a 1inch pine board is possible even with the crudest .22