In firearms terminology, the firearm frame or receiver is the part of a firearm which integrates other components by providing housing for internal action components such as the hammer, bolt or breechblock, firing pin and extractor, and has threaded interfaces for externally attaching ("receiving") components such as the barrel,

stock In finance, stock (also capital stock) consists of all the shares by which ownership of a corporation or company is divided.Longman Business English Dictionary: "stock - ''especially AmE'' one of the shares into which ownership of a company ...

, trigger mechanism and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in fr ...

optical sight A sight is an aiming device used to assist in visually aligning ranged weapons, surveying instruments or optical illumination equipments with the intended target. Sights can be a simple set or system of physical markers that have to be aligne ...

s. The receiver is often made of

forge A forge is a type of hearth used for heating metals, or the workplace (smithy) where such a hearth is located. The forge is used by the smith to heat a piece of metal to a temperature at which it becomes easier to shape by forging, or to the ...

d, machined, or stamped steel or aluminium; in addition to these traditional materials, modern science and engineering have introduced

polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic ...

s and

sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

metal powders to receiver construction.

Mounting

A barrel can be fixed to the receiver using barrel and receiver action threads or similar methods.

In US law

For the purposes of

United States law The law of the United States comprises many levels of codified and uncodified forms of law, of which the most important is the nation's Constitution, which prescribes the foundation of the federal government of the United States, as well as ...

, the receiver or frame is legally the firearm, and as such it is the controlled part. The definition of which assembly is the legal receiver varies from firearm to firearm, under US law. Generally, the law requires licensed manufacturers and importers to mark the designated receiver with a

serial number A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it. Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist en ...

, the manufacturer or importer, the model and caliber. In addition, makers of receivers are restricted by

International Traffic in Arms Regulations International Traffic in Arms Regulations (ITAR) is a United States regulatory regime to restrict and control the export of defense and military related technologies to safeguard U.S. national security and further U.S. foreign policy objectiv ...

. Thus, in the case of a firearm that has multiple receiver parts (such as the AR-15, which has an upper and a lower receiver), the legally controlled part is the one that is serialized. For the AR-15 rifle, the lower receiver assembly is legally considered the actual receiver (although it is functionally a

chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpar ...

that also houses the separate

trigger Trigger may refer to: Notable animals and people ;Mononym * Trigger (horse), owned by cowboy star Roy Rogers ;Nickname * Trigger Alpert (1916–2013), American jazz bassist * "Trigger Mike" Coppola (1900–1966), American gangster ;Surname * ...

group); while in the

FN-FAL The FAL (a French acronym for (English: "Light Automatic Rifle")), is a battle rifle designed in Belgium by Dieudonné Saive and manufactured by FN Herstal (simply known as FN). During the Cold War the FAL was adopted by many countries of the ...

rifle, it is the upper assembly that is serialized and legally considered the receiver. This has led to prosecutors dropping charges against illegal manufacturing of AR-type firearms to avoid court precedents establishing that neither the upper nor the lower receiver individually contain all the components to be legally classified as a firearm.

Unfinished receivers

"Unfinished receivers", also called "80 percent receivers" or "blanks", are partially completed receivers with no serial numbers. Purchasers must perform their own finishing work in order to make the receiver usable. The finishing of receivers for sale or distribution by unlicensed persons is against US law. Because an unfinished 80% receiver is not a firearm, purchasers do not need to pass a background check. The resulting firearm is sometimes called a " ghost gun".

3D printed receivers

, two designs for 3D printable polymer lower receivers for the AR-15 have been released: the AR Lower V5 and the

Charon In Greek mythology, Charon or Kharon (; grc, Χάρων) is a psychopomp, the ferryman of Hades, the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the wo ...

. Like unfinished receivers, 3D-printed ones can be used to produce ghost guns. (Again under US law, the printed receiver itself is a firearm.)

References

{{Firearm accessories mounting standards Firearm components