Rail - A metal track installed in the fore-end of weapon to accept a hand stop or sling.

Ram - The main shaft of a metallic cartridge reloading press.

Ramp / Sight Ramp - The steel base on which some sights are mounted.

Range - The distance between the shooter and the target. Also short for shooting range.

Rangefinder - Device for determining range, or for optically measuring ( or estimating ) the direct distance to a target.

Ranging - The technique that a sniper uses to compensate for bullet trajectory by adjusting the ballistic cam of an adjustable/ranging telescope.

Rate Of Twist - In a barrel, the length over which the rifling grooves make one complete twist ( i.e. the length of the bore used to turn the bullet one full revolution ) e.g. 1:10 or one revolution in 10 inches. Differs from calibre to calibre. Bullet weight must be appropriate to the rate of twist or bullets will not stabilise in flight. The heavier the bullet, thus the longer, the faster the twist rate must be. See Greenhill’s formula.

Rebated Rim - See Rim

Receiver - The basic unit of a firearm which houses the firing and breech mechanism and to which the barrel and stock are assembled, i.e. the rigid metal housing which contains the working parts of the action ( bolt, striker, trigger mechanism, etc. ). Called the “breech body” in England. In revolvers, pistols and break-open shotguns, it is called the frame.

Receiver Sight - See Peep sight.

Rechamber - To alter the chamber of a barrel to take a cartridge other than the original, e.g. reaming out a .308 Win chamber to .30-06 dimensions. Can only be done for cartridges having the same bullet diameter, e.g. 7X57 to 7X64.

Recoil - The rearward thrust of a firearm caused by the propulsion of a projectile in the opposite direction. Refer Newton’s 3rd Law of Physics: for every action there is an equal but opposite reaction. Commonly called “kick”. The amount of recoil felt by the shooter depends on factors such as the weight of the rifle ( which absorbs some of the recoil ), the design of the stock, the shooting position, etc. Incidentally complete analysis based on conservation of momentum would have to include the angular momentum the bullet acquires, which depends on the twist rate and length of the barrel...

Recoil Lug - The heavy metal protrusion beneath the front of the action designed to stabilize the action in the stock and transfer the recoil to the stock.

Recoil Operated - An automatic or semiautomatic type firearm in which the force of recoil is used to unlock the breech bolt and then to complete the cycle of extracting, ejecting and reloading, as opposed to Gas operated.

Recoil Pad - A rubber or leather pad at the end of the butt to absorb recoil. Can also be some kind of pad on the shoulder of the shooter to absorb the recoil.

Regulate / Barrel Regulation - In double-barrel rifles, the process of getting both barrels to shoot to the same point of impact with a given load at a given distance. This is normally done to around 70 metres. The further away from this regulated distance one shoots, the more one must compensate for left/right point of impact.

Reload - See Handload.

Remaining Energy - A projectile's energy in foot pounds at a given range.

Repeater - A firearm capable of being fired several times without loading extra ammunition into the firearm. Usually applied to rifles and carbines. Any firearm equipped with a magazine.

Retina - The light-sensitive layer at the back of the eye. It consists of rod (black/white sensitive for night vision) and cone (colour sensitive for day vision) cells.

Resize - In reloading ammunition, the forcing of the fired case into a sizer die to reduce to its original ( unfired ) dimensions ( it swells in the chamber when fired ). See also Neck (re)sizing.

Resizing Die - The reloading die that resizes fired cartridge cases and removes spent primers by means of a decapping pin.  See dies.

Reticle / Reticule - 1. In telescopic sights, the element which is optically referred to the target. It may consist of straight or tapered cross-hairs (wires in the tube forming a central cross ), dots, or other marks used to determine the point-of-aim, size of, or range to the target.
                                    2. Markings in a microscope eyepiece used to establish location or scale. Commonly used to measure rifling.

Rifle Cant - Any leaning of the rifle to the left or right from a vertical position during firing. This should be eliminated because of the potential for increasing misses at longer ranges.

Rifling - Spiral grooves in the bore of a barrel to impart a rotary motion ( spin ) to the bullet to provide it with rotational stability. This will ensure that the bullet flies true with a point-first attitude..  Methods of manufacturing are Button rifling, Cut rifling and Hammer forging.  See Lands, Rate of Twist.

Rim - On a cartridge case, the lip or flange around the case head, which provides purchase for the extractor claw. Initially all cases had projecting rims, i.e. rims larger in diameter than the case body, e.g. .303 ( today these are known as "rimmed" or "flanged" cases ). The Mauser bolt action with its ( then ) unique extractor system gave us the "rimless" case, e.g. 7X57, .30-06, which is not really rimless, but has a non-projecting rim of the same diameter as the case body. The rim is formed by a groove cut around the periphery of the case head. "Rebated rims" are smaller in diameter than the case body ( .425 Westley Richards ), as well as "semi-rimmed" cases ( only slightly larger in diameter than the case body, but also with an extractor groove ) e.g. .220 Swift. ( Click here for picture. )

Rimfire - A flange-headed cartridge ( e.g. .22LR ) which has its priming compound in the hollow rim of the case ( the rim is in the form of a fold in the drawn brass, which is very thin ). The firing pin can strike anywhere on the rim. Opposed to Centre-fire cartridges, these cannot be reloaded.

Rings - ( Not Scope rings. )  Circular marks around the case, due to poor reaming of the chamber.

Rolling Block - Single shot action in which a breech block and hammer each rotate about their separate transverse pins in the receiver. The two members are swung rearward, away from the barrel breech to load the mechanism or extract a cartridge case. To fire a cartridge, the breech block is closed and locking is accomplished by the falling hammer engaging an abutment on the breech block.

Rotary Magazine See Magazine

Round - Another word for Cartridge.

Round Nose - (Bullet) Abbreviation RN.  A bullet design which features a rounded nose.

Ruptured Case - Cartridge case that splits or bursts open on firing, due to problems such as excessive headspace, oversized chamber, fatigued or brittle brass, etc. Extremely dangerous, as the escaping gases can blind or otherwise injure the shooter.

Running Game Target - An Olympic Shooting event whereby competitors shoot 22 calibre rifles at life-sized lithographs of a boar with a target superimposed on it. The target moves on a track at various speeds and the shooter must track each target and fire before it disappears. (abbr. RGT).

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