In firearms terminology and at law, 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, trigger mechanism and iron/optical sights.
The receiver is often made of forged, machined, or stamped steel or aluminium. Apart from these traditional materials, modern techniques have introduced polymer and sintered metal powder receivers to the market.
A barrel may typically be affixed to a firearm receiver using barrel and receiver action threads or similar methods.
See also: Parts kit
For the purposes of United States law, 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, the manufacturer or importer, the model and caliber. Makers of receivers are restricted by International Traffic in Arms Regulations. 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 that also houses the separate trigger group. In the FN-FAL 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", 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 called a privately made firearm.
Though the ATF during the Biden Administration attempted to restrict the sale and marketing of unfinished receivers and kits containing them, a federal court in Texas held the regulations exceeded the agency's statutory authority. The regulation of unfinished receivers and receiver kits was vacated nationwide on June 30, 2023, keeping them unregulated and legal in interstate commerce.
As of 2015[update], two designs for 3D printable polymer lower receivers for the AR-15 have been released: the AR Lower V5 and the Charon. Like unfinished receivers, 3D-printed designs may be used to produce ghost guns.
Firearm frame or receiver. That part of a firearm which provides housing for the hammer, bolt or breechblock, and firing mechanism, and which is usually threaded at its forward portion to receive the barrel.
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