AR-15–style rifle
An AR-15–style rifle is a lightweight semi-automatic rifle based on or similar to the Colt AR-15 design. The Colt model removed the selective fire feature of its predecessor, the original ArmaLite AR-15, which is a scaled-down derivative of the AR-10 design. It is closely related to the military M16 rifle.
ArmaLite sold the patent and trademarks for both to Colt's Manufacturing Company in 1959 after the military rejected the design in favor of the M14. After most of the patents for the Colt AR-15 expired in 1977, many firearm manufacturers began to produce copies of the rifle under various names. While the patents are expired, Colt has retained the trademark to the AR-15 name and is the sole manufacturer able to label their firearms as such.
From 1994 to 2004, the Federal Assault Weapons Ban restricted the sale of the Colt AR-15 and some derivatives in the United States, although it did not affect rifles with fewer listed features. After the phrase "modern sporting rifles", to be used synonymously with the AR-15 style, was coined in 2009 by the US National Shooting Sports Foundation, a firearms trade association, it was quickly adopted by much of the industry.
Beginning in the 2010s, AR-15–style rifles became one of the "most beloved and most vilified rifles" in the United States, according to The New York Times; the rifles have gained infamy due in part to their use in high-profile mass shootings. Promoted as "America's rifle" by the National Rifle Association of America, their popularity is partially attributable to [|active restrictions], or proposals to ban or restrict them. They are emblematic as being on the frontline of the debate over U.S. gun control.
Terminology
Different sources attribute the letters "AR" in AR-15 to different origins in the early history of the rifle by its manufacturer, ArmaLite. According to the company's website, it stood for "ArmaLite Rifle". According to Eugene Stoner's business partner, Jim Sullivan, the letters "AR" stood for the first two letters of the company's name, while according to Stoner's daughter and son-in-law it stood for "ArmaLite Research". "AR-15" is most-commonly used to refer only to the civilian semi-automatic variants of the rifle which lack the fully automatic function. A common misconception is that "AR" is an abbreviation for "assault rifle" or "automatic rifle", perhaps because of the weapon's inclusion in the Federal Assault Weapons Ban in 1994, or because the ArmaLite AR-15 was originally designed to replace the M14 rifle in the Vietnam War.The AR-15 is closely related to the military M16 and M4 carbine rifles, which all share the same core design. Invented by infantry rifle designer Eugene Stoner in 1956 for use in the 7.62 NATO caliber ArmaLite AR-10 battle rifle, the design features a gas-operated, rotating bolt combined with an integral piston, and was patented under. A lighter weight selective fire variant of the AR-10 was designed in 1958 for military use and designated the ArmaLite model 15, or AR-15. Due to financial problems and limitations in terms of manpower and production capacity, ArmaLite sold the AR-15 and AR-10 designs and trademarks to Colt in 1959.
In 1964, Colt began selling its own version with an improved semi-automatic design known as the Colt AR-15. After Colt's patents expired in 1977, an active marketplace emerged for other manufacturers to produce and sell their own semi-automatic AR-15–style rifles. Some versions of the AR-15 were classified as "assault weapons" and banned under the Federal Assault Weapons Ban in 1994 within the United States. This act expired in 2004.
In 2009, the term "modern sporting rifle" was coined by the National Shooting Sports Foundation for its survey that year as a marketing term used by the firearms industry to describe modular semi-automatic rifles including AR-15s. Today, nearly every major firearm manufacturer produces its own generic AR-15–style rifle. As Colt continues to own and use the AR-15 trademark for its line of AR-15 variants, other manufacturers must use their own model numbers and names to market their AR-15–style rifles for commercial sale.
Under US law, a firearm with a barrel length of less than and an overall length of less than, that was not made from a rifle, is not considered to be a short-barreled rifle. As the inclusion of a shoulder stock constitutes "intent to fire from the shoulder" and thus reclassifies the firearm as a rifle, many gun manufacturers offer AR-15–style "pistol" versions that are manufactured to be sold stockless or with a stabilizing pistol brace. If a firearm was originally manufactured as a rifle, it can't be converted into a pistol. However, if the firearm was originally a pistol, the resulting firearm with an attached shoulder stock is not an NFA firearm if it has a barrel of or more in length, and such rifle may be reconfigured as a pistol legally.
The lower receiver alone is legally defined as a firearm under United States federal law. However, the legality of this definition has been disputed in conflicting court rulings as to whether the AR-15 lower receiver matches the legal definition set forth in 27 CFR § 479.11, with some lower courts disagreeing while a 2021 case from the Eighth Circuit found otherwise.
Modularity and customization
While most earlier breech-loading rifles had a single receiver housing both the trigger and reloading mechanism, an innovative feature of the AR-15 was modular construction to simplify substitution of parts and avoid need for arsenal facilities for most repairs of malfunctioning military rifles. A distinctive two-part receiver is used by both military and sporting AR-15–style rifles.As civilian ownership of AR-15–style rifles became sufficient to create a market for improvements, numerous manufacturers began producing aftermarket parts—including parts with features not found on basic AR-15 rifles, and individuals with basic mechanical aptitude can often substitute these pieces for original equipment without needing a gunsmith. Due to the vast assortment of aftermarket parts and accessories available, AR-15–style rifles have also been referred to as "the Swiss Army knife of rifles", "Barbie Dolls for Guys", or "LEGOs for adults". These more or less interchangeable modules are a defining characteristic of AR-15–style rifles.
The lower receiver includes the trigger guard in front of the detachable pistol grip, and behind the magazine well. Lower receivers may be bought "stripped"—a single solid part and legally a firearm in the United States, albeit nonfunctional, with no fire control group or lower parts kit installed. End users may install their own choice of fire control group and lower parts kit. The lower receiver holds the trigger assembly including the hammer, and is the attachment point for the buttstock. The lower receiver is attached to the upper receiver by two removable pins. Disassembly for cleaning or repair of malfunctions requires disengaging these pins from the upper receiver. Releasing the rear take-down pin allows the receiver to be opened by rotation around the forward pivot pin as a hinge. Releasing the front pin as well allows the upper receiver to be separated from the lower for cleaning, maintenance or change of caliber by installation of a different upper receiver assembly.
The upper receiver contains the bolt carrier assembly and is attached to the barrel assembly. Sights may be attached to the upper receiver or the barrel assembly. A handguard usually encloses the barrel and is attached to the upper receiver, and depending on the handguard, also attached to the barrel's gas block.
Folding stocks
AR-15–style rifles may have folding or collapsible stocks which reduce the overall length of the rifle when folded, although some designs of the stock folding device may not allow the firearm to be fired until unfolded, or only fire once until unfolded. A few manufacturers have made full upper receivers, or even "bufferless" bolt carrier systems where the buffer system is wholly contained in the upper receiver, and therefore does not use the buffer tube, which allows for firing while the stock is in the folded position, or removal of the stock altogether.Gas systems
The standard design includes a gas block and tube to vent burnt powder gas back into the bolt carrier assembly where it expands in a variable volume chamber forcing the bolt open to eject the spent cartridge case. The buffer spring in the buttstock then pushes the bolt closed after picking up a new cartridge from the magazine. This Stoner bolt and carrier piston system has the disadvantage of venting un-burned smokeless powder residue into the receiver where it may ultimately accumulate in quantities causing malfunctions. Some AR-15–style rifles use an alternative short-stroke gas piston design borrowed from the ArmaLite AR-18, where a metal rod pushes against the bolt carrier, driven by a piston located just behind the barrel gas port. This piston design keeps the rifle cleaner by not exhausting in to the receiver. Other AR-15–style rifles feature redesigned gas systems so the rifle is "over-the-beach capable", allowing it fire safely as quickly as possible after being submerged in water. The original design features a free-floating firing pin. To theoretically reduce the risk of slam-firing, the HK416 and its civilian variant MR556 feature a proprietary firing pin safety in the bolt. Such firing pin safeties may obstruct the upper from working with standard AR-15-type full height hammers located in the fire control group of the lower.Left-handed users
Most rifles eject spent cartridges from the right side of the receiver away from right-handed shooters who place the butt against the right shoulder while sighting with the right eye and using a finger of the right hand to pull the trigger. Right-side ejection is a disadvantage for the third of the population whose left eye is dominant, and for the tenth of the population who are left handed, because holding these rifles against their left shoulder for maximum accuracy may cause the rifle to eject hot spent cases toward the chest, neck, or face of a left handed shooter. When the M16A2 was adopted by the Army in 1986, it incorporated a built-in brass deflector to keep ejected cartridges from hitting the user. Most civilian variants also copy that feature. The modular design of AR-15–style rifles has encouraged several manufacturers to offer specialized parts including leftward ejecting upper receivers and left-handed bolts/bolt carriers for converting right-handed AR-15–style rifles for left-handed use.Ambidextrous lower receivers, magazine releases, and safety selectors have also been produced, allowing release of the magazine from the left side, closing of the bolt from the right side, and operation of the safety from the right side, respectively.