Rifle Terminology; Rifle - U.S.A. legal description and definition - A shoulder fired gun having a barrel length of at least 16 inches with rifling in the barrels bore, or a barrel having a rifled bore. Barrel - The part of the rifle through which projectiles pass in their travel from the chamber or breech to the muzzle. Bore - The interior of a rifle's barrel excluding the chamber. Breech - In modern firearms, that portion of the rifle barrel through which the cartridge is inserted. Caliber - The nominal diameter of a projectile of a rifled firearm or the diameter between lands in a rifled barrel. Chamber - The rear part of the rifle barrel that is formed to accept the cartridge to be fired. Muzzle - The forward end of a rifle barrel; the point from which the projectile leaves the barrel. Rifling - Spiral grooves in a gun's bore that consist of lands and grooves which spin the projectile in flight and impart accuracy. Rifling is present in all true rifles. Throat - The unrifled forward portion of the chamber, tapered to meet the rifle barrel bore. Breech Loader - Any rifle in which the loading is accomplished from the breech. Muzzle loader - Any rifle with a solid breech, thereby necessitating loading through the muzzle of the rifle. Air-Rifle - A rifle that propels a projectile by compressed air. Center-Fire Rifle - A rifle cartridge which has a centrally located primer in the base of the case, which is for the most part removable. (Reloadable) Rim-Fire Rifle - A rifle cartridge which contains the priming mixture within the rim of the base of the cartridge. (Not Reloadable) Flint Ignition - Where flint strikes a piece of steel making sparks to ignite a powder charge. Percussion Cap Ignition (Rim-Fire) - Where a percussion cap is placed over a nipple and a hammer must strike the rim of the cap to ignite a powder charge in the barrel. Primer Ignition (Center-Fire) - Where a modern design center-fire primer must be struck in the center by a hammer or firing pin to ignite a powder charge in the barrel. Action - The working mechanism of a rifle of which there are several types that may mechanically load and or fire ammunition. Automatic Action - A rifle mechanism designed to feed cartridges, fire them, eject their empty cases and repeat this cycle as long as the trigger is depressed. Bolt Action - A rifle mechanism activated by manual operation of the breech block that resembles a common door bolt. Break Action - A rifle mechanism lacking a magazine where separately carried ammunition must be manually placed in the rifles chamber or chambers for each firing. Lever Action - A rifle mechanism activated by manual operation of a lever. Semi-Automatic Action - A rifle mechanism designed to fire a single cartridge, eject the empty case and reload the chamber each time the trigger is pulled. Sidelock - A type of action, where the moving parts are located on the side lock plates inletted in the stock. Slide Action - A rifle mechanism activated by manual operation of a horizontally sliding handle almost always located under the barrel. "Pump action" is a synonym for "slide action".