Firearm Glossary

rolling block: A form of firearm action where the sealing of the breech is done with a circular shaped breechblock able to rotate on a pin. The breechblock is locked into place by the hammer, thus preventing the cartridge from moving backwards at the moment of firing. By cocking the hammer, the breechblock can be rotated freely to reload the weapon.

rimfire: A type of firearm cartridge that used a firing pin to strike the base's rim, instead of striking the primer cap at the center of the base of the cartridge to ignite it (as in a centerfire cartridge). The rim of the rimfire cartridge is essentially an extended and widened percussion cap that contains the priming compound, while the cartridge case itself contains the propellant powder and the projectile (bullet).

rifling: Helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis. This spin serves to gyroscopically stabilize the projectile, improving its aerodynamic stability and accuracy.

rifle bedding: a process of filling gaps between the action and the stock of a rifle with an epoxy based material.

ricochet: is a rebound, bounce or skip off a surface, particularly in the case of a projectile.

revolver: a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing.

Reflector (reflex) sight: A generally non-magnifying optical device that has an optically collimated reticle, allowing the user to look through a partially reflecting glass element and see a parallax free cross hair or other projected aiming point superimposed on the field of view. Invented in 1900 but not generally used on firearms until reliably illuminated versions were invented in the late 1970s (usually referred to by the abbreviation "reflex sight").

Red dot sight a type of reflector (reflex) sight for firearms that gives the uses a red light-emitting diode as a reticle to create an aimpoint.

recoil operation: Recoil operation is an operating mechanism used in locked-breech, autoloading firearms. As the name implies, these actions use the force of recoil to provide energy to cycle the action.

recoil: The backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile, according to Newton's third law. (often called kickback or simply kick)

receiver: the part of a firearm that houses the operating parts.

rate of fire: the frequency at which a firearm can fire its projectiles.

pump-action: A rifle or shotgun in which the handgrip can be pumped back and forth to eject a spent round of ammunition and to chamber a fresh one. It is much faster than a bolt-action and somewhat faster than a lever-action, as it does not require that the shooter remove their trigger hand during reloading. In rifles, this action is also commonly called a slide action.

POI: point of impact.

POA: point of aim.