A Pen gun is a disguised firearm that resembles an ink pen. They generally are of small caliber (e.g., .22LR, .25ACP, .32 ACP, .38-caliber, etc.) and are single shot. Early examples of pen guns were pinfired, but modern designs are rim or centerfire. Some pen guns are not designed to fire regular cartridges, but rather blank cartridges or tear gas...