I designed this gun around the 22-caliber long rifle cartridge for several reasons. They are easy to get, most sporting goods stores carry them, and they are inexpensive. They are also easy to hide and if stored in a cool, dry place, they may last as long as 50 years. You can literally carry hundreds of them in your pocket. Also, they have a low chamber pressure, which makes them safer for use in homemade firearms. The term “Rim Fire”, means just that. A sharp blow to the rim at the base of the cartridge will crush the rim, igniting the explosive primer compound, which then lights the gunpowder.