The barrel is the tube down which fired ammunition is stabilised before exiting the firearm. In general terms, the longer the barrel, the further the bullet will travel, however there is a point at which the resistance offered by the friction of the barrel will counterbalance the expansion of the gasses from the cartridge. Most modern rifles and shotguns have barrels between 14" and 22", although some older hunting rifles had much longer barrels. Most modern pistols have barrels between 2" and 12", this figure hasn't changed much though the history of firearms due to the nature of pistols as a PDW or secondary armament.