# Receiver (firearms)

In firearms terminology and 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. Some firearm designs, such as the AR-15 platform, feature receivers that have 2 separate sub-assemblies called the upper receiver which houses the barrel/trunnion, bolt components etc and the lower receiver (Trigger Mechanism Housing in some cases) that holds the fire control group, pistol grip, selector, stock etc.
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.

## Mounting

A barrel may typically be affixed to a firearm receiver using barrel and receiver action threads or similar methods.

## In US law

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

"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 known as a "ghost gun".
During the Biden Administration, the ATF imposed regulations on the sale and marketing of unfinished receivers and kits containing them by revising the legal definition of receivers to include "a partially complete, disassembled, or nonfunctional frame or receiver, including a frame or receiver parts kit, that is designed to or may readily be completed, assembled, restored, or otherwise converted to function as a frame or receiver". (The term "receiver" was also redefined as referring to non-handgun firearms, while "frame" was redefined as referring to handguns exclusively.) The new definitions went into effect on August 24, 2022. In the case VanDerStok v. Garland, filed on June 30, 2023, a federal court in Texas ruled that the new ATF regulations exceeded the agency's statutory authority, and struck them down. However, on August 8, 2023, the Texas court's nationwide vacatur was temporarily placed on hold by the Supreme Court of the United States, leaving the new ATF regulations on unfinished receivers in place.

## 3D printed receivers

As of 2024, several designs and at least two designs for 3D printable polymer lower unfinished receivers for the AR-15 have been released: the AR Lower V5 and the Charon. 3D printed designs may also be used to produce privately made firearms.
| Name | Date made public | Type | Process | Designer | Caliber |
| AR Lower V5 | 2013-032013, March | Receiver: AR-15 rifle lower receiver | FDM | Defense Distributed | .223 Rem/ 5.56x45 |
| The receiver was able to handle enough stress to fire more than 600 rounds. |||||
| Charon | 2013-05May 2013 | Receiver: AR-15 rifle lower receiver | FDM | WarFairy | .223 Rem/ 5.56x45 |
| Charon V3 weighs 0.2 pounds and showed no signs of strain after 96 rounds of 5.56 AR-15 ammo were fired. |||||
| WarFairy P-15 | 2013-052013, May | Receiver: AR-15 rifle lower receiver | FDM | WarFairy | .223 Rem/ 5.56x45 |
| Hanuman AR-15 Bullpup | 2014-052014, May | Receiver: AR-15 rifle bullpup lower receiver | FDM w/ ABS | WarFairy | .223 Rem/ 5.56x45 |
| According to the creators, "It requires a bufferless upper to function, such as the ARAK-21 or Rock River Arms PDS Carbine, or a regular upper with a CMMG Style .22 LR Conversion installed." |||||
| Ruger Charger | 2014-072014, July | Receiver: Ruger 10/22 semi-automatic pistol | FDM | "Buck-o-Fama" (pseudonym) | .22 Long Rifle |
| A pistol version of the popular Ruger 10/22 rifle. |||||
| CM901 | 2015-032015, March | Receiver: AR-10 Receiver | FDM | Printed Firearm | 7.62×51mm |
| Based on Colt CM901. |||||
| Lopoint / Bigpoint | 2019, November (v1); 2020, November (,40/.45); 2021, May (v2) | Frame: Hi-Point pistol frame | FDM | CTRLPew / Atmac / freeman1337 | 9×19mm Parabellum, .380 ACP, .40 S&W, .45 ACP |
| Compatible with Hi-Point C9, CF380, JCP, and JHP parts. Extremely cheap due to the high availability of the required parts kits. |||||
| Scz0rpion | 2020, October | Receiver: CZ Scorpion Evo 3 receiver | FDM | Are We Cool Yet? | 9×19mm Parabellum |
| First 3D printed frame to be successfully tested with 1000+ rounds full auto in one sitting without failure. |||||
| 3011 / 3011DS | 2021, November; 2023, January (DS) | Receiver: 1911 based PDW | FDM | Deterrence Dispensed | .45 ACP, 9×19mm Parabellum, .22 TCM |
| Utilizes a 1911 slide for the upper, and an AR-15 fire control group. An updated version, called the 3011DS, allows the use of double-stack higher capacity Remington and RIA magazines. |||||
| 3DPD10 | 2023, April | Frame: Pistol frame | FDM | Avidity Arms | 9×19mm Parabellum |
| A 3D-printable frame for the Avidity Arms PD10. This design is notable as the first firearm released by commercial company designed to be 3D printed. |||||

## In Canadian law

The receiver or frame is legally the firearm, and as such it is the part that requires a manufacturer's serial number and valid Possession and Acquisition Licence to acquire and own. In the case of a handgun frame or revolver frame, it is the part that requires a Restricted-class PAL (RPAL), and registration.