rail
A rail is an attachment point on a firearm. Rails can be used to attach a variety of accessories such as sights, flashlights, and foregrips.
For more information, please refer to the topic page on rails.
For more information, please refer to the topic page on rails.
rangefinding reticle
A weapon sight equipped with a rangefinding reticle assists the shooter in determining the range to a target. Rangefinding reticles are different from electronic rangefinders, as electronic rangefinders use a laser or sonar to determine distance while rangefinding reticles do not need any electronics at all, instead determining range based on the appearance of an object with a known size.
In most cases, rangefinding reticles determine distance based on the average size of a standing adult male, approximately 5' 10". The shooter takes aim at a standing adult male, and is able to determine range to the target based on how large the target appears in the scope relative to reference points in the rangefinding reticle.
Rangefinding reticles are used on both fixed and variable-magnification sights. In variable-magnification sights, the rangefinding reticle will only be accurate when the sight is set to a "default" magnification determined by the sight's manufacturer, or when the shooter performs a mathematical calculation to compensate for the adjusted magnification. Alternatively, some sights keep magnification of the sight picture and the sight's reticle identical, so that the reticle is much more difficult to view at low magnification, but the rangefinging measurements stay the same regardless of the level of magnification.
Common rangefinding reticles include the mil dot reticle, the 400m Simonov reticle, and the 1000m Dragunov reticle.
In most cases, rangefinding reticles determine distance based on the average size of a standing adult male, approximately 5' 10". The shooter takes aim at a standing adult male, and is able to determine range to the target based on how large the target appears in the scope relative to reference points in the rangefinding reticle.
Rangefinding reticles are used on both fixed and variable-magnification sights. In variable-magnification sights, the rangefinding reticle will only be accurate when the sight is set to a "default" magnification determined by the sight's manufacturer, or when the shooter performs a mathematical calculation to compensate for the adjusted magnification. Alternatively, some sights keep magnification of the sight picture and the sight's reticle identical, so that the reticle is much more difficult to view at low magnification, but the rangefinging measurements stay the same regardless of the level of magnification.
Common rangefinding reticles include the mil dot reticle, the 400m Simonov reticle, and the 1000m Dragunov reticle.
receiver
The receiver is the heart of a rifle or shotgun. It is the main housing that connects the firearm's feed system, barrel, stock, and FCG, allowing all the components to function together. In almost all cases, the receiver is the regulated portion of the firearm, meaning that it is the key component of the firearm that is taxed, tagged, and tracked by the authorities. The receiver is regulated because without it, everything else on the firearm is harmless machine parts.
In some cases, the receiver is separated into two parts, typically called an "upper" and a "lower." Most shooters have been exposed to this concept through the AR pattern rifles, but many other firearms have uppers and lowers, such as the FN FAL and the MAC M-10. When a firearm has an upper and a lower receiver, the BATF will decide on which part will be the regulated part based on an analysis of the design. For example, the AR and M-10 have regulated lowers, while the FAL has regulated uppers.
See also: frame, slide
In some cases, the receiver is separated into two parts, typically called an "upper" and a "lower." Most shooters have been exposed to this concept through the AR pattern rifles, but many other firearms have uppers and lowers, such as the FN FAL and the MAC M-10. When a firearm has an upper and a lower receiver, the BATF will decide on which part will be the regulated part based on an analysis of the design. For example, the AR and M-10 have regulated lowers, while the FAL has regulated uppers.
See also: frame, slide
rifling
Rifling is a set of spiraling grooves cut down the length of the bore. When a bullet is fired and travels down the barrel, the hard steel of the rifling grips the softer bullet and keeps it concentric to the bore, as well as imparting spin to keep the bullet on course as it exits the barrel. Rifling is the key to accuracy, as older non-rifled firearms fired round projectiles that bounced around as they traveled down the bore and exited without spin, limiting accuracy to about 100 meters. A modern hunting rifle is accurate out to 600 meters or more, and specialized rifles can extend that range to well beyond 1000 meters.
For more information, please refer to the topic page on rifling.
For more information, please refer to the topic page on rifling.
rimfire
Rimfire cartridges do not have a distinct "button"-shaped primer like centerfire cartridges, instead having their primer incorporated into a the rim of the cartridge's base. Rimfire ammunition is ignited when the rim of the cartridge is struck by the firing pin, which is often shaped like a plate or hammer, whereas centerfire firing pins are usually shaped like thick, blunt needles.
Rimfire cartridge cases are not as strong as centerfire cases because the cartridge lacks an integral base (the base is the primer). Because of this limitation, rimfire cartridges are loaded with small, light bullets and fairly light powder charges, making them useful for inexpensive plinking and small game hunting but unpopular for self-defense. The most common rimfire cartridge by far is .22LR (long rifle), although there are a few other popular rimfires such as the .22 WMR and .17 HMR.
Due to way the primer is made and attached to the cartridge base, rimfire cartridges cannot be easily reloaded. However, most rimfire cartridges are so inexpensive that only very minimal savings could be had by reloading.
Rimfire cartridge cases are not as strong as centerfire cases because the cartridge lacks an integral base (the base is the primer). Because of this limitation, rimfire cartridges are loaded with small, light bullets and fairly light powder charges, making them useful for inexpensive plinking and small game hunting but unpopular for self-defense. The most common rimfire cartridge by far is .22LR (long rifle), although there are a few other popular rimfires such as the .22 WMR and .17 HMR.
Due to way the primer is made and attached to the cartridge base, rimfire cartridges cannot be easily reloaded. However, most rimfire cartridges are so inexpensive that only very minimal savings could be had by reloading.
rings (scope rings)
Rings are used to attach a sight to a rail. A few sights have a rail mount machined into the sight body, but this means that the sight can only ever be attached to the style of rail the sight was manufactured to use. Instead, most sights are designed to use rings so that the sight can be mounted on a variety of different rails by simply swapping the style of the rings.
RMR (Ruggedized Miniature Reflex)
RMR is an abbreviation for Ruggedized Miniature Reflex, a label trademarked by the Trijicon Corporation but often used to describe any highly compact dot sight. RMRs are intended to be mounted on pistols, but can be used on any weapon platform where low weight and small profile are a priority.
round
Round is an informal term for all types of ammunition, as well as the projectiles they propel. It is acceptable to say "I have 50 rounds left" meaning that you have 50 cartridges remaining, regardless of whether those cartridges are for a shotgun, pistol, or rifle. It is equally acceptable to say "I put about 50 rounds downrange" to indicate that projectiles of any type were fired.
See also: cartridge, shell
See also: cartridge, shell
RPK (RPKM, RPK-74)
The RPK (Ruchnoy Pulemyot Kalashnikova, or "Kalashnikov's hand-held machine gun") is a Russian automatic rifle intended to bridge the gap between assault rifles and belt-fed support weapons. The RPK can be simply described as an AK rifle on steroids, featuring a heavier barrel, finer sights, a heavier stock and forearm, and a strengthened receiver stamped from 1.5mm steel plate (standard AK receivers are stamped from 1mm steel plate). The RPK accepts the AK's standard 30 round magazines, but was intended to use larger 45 and 75 round magazines.
RPKs and RPK-pattern firearms are produced at the Molot factory in Russia, whereas AK and AK-pattern firearms are produced at the Izhmash factory. RPK-pattern firearms are imported into the United States under the "Vepr" name.
RPKs and RPK-pattern firearms are produced at the Molot factory in Russia, whereas AK and AK-pattern firearms are produced at the Izhmash factory. RPK-pattern firearms are imported into the United States under the "Vepr" name.
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