Receiver ( Firearms ) - wikipedia Receiver ( Firearms ) Disassembled Mauser action showing partially disassembled receiver and bolt In firearms terminology, the firearm receiver or firearm frame is the part of a firearm which provides housing for internal components such as the hammer, bolt or breechblock, action and firing mechanism, and is usually threaded at its forward portion to `` receive '' the barrel and has screw holes on the bottom and / or rear to receive the stock and grip. The receiver is often made of forged, machined or stamped steel or aluminium ; in addition to these traditional materials, modern science and engineering have introduced polymers and sintered metal powders to receiver construction. Contents 1 In US law 1.1 Unfinished receivers 2 Notable receivers 3 References In US law AR - 15 rifles showing their configurations with different upper receivers ( stripped - down lower receiver is visible at bottom ) 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. In addition, makers of receivers are restricted by International Traffic in Arms Regulations. Thus, in the case of a firearm that has multiple receivers ( such as the AR - 15, which has an upper and lower receiver ), the legally controlled part is the one that is serialized. For the AR - 15 rifle, the lower assembly is considered the legal receiver ; while in the FN - FAL rifle, it is the upper assembly that is serialized and considered the legal receiver. 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 ''. An AR - 15 variant made from an 80 % receiver was used in the 2013 Santa Monica shooting. Notable receivers Two 3D printed polymer lower receivers for the AR - 15 have been released : the AR Lower V5 and the Charon. References Jump up ^ `` 27 CFR 478.11 : Meaning of terms ''. US Government. 2016. Retrieved 16 September 2016. 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. Jump up ^ `` HK416 modular assault rifle / carbine / upper receiver assembly ( Germany ) ''. Retrieved 5 Aug 2010. Jump up ^ `` Firearms - Frequently Asked Questions - Firearms Technology ATF ''. Archived from the original on 3 May 2015. Retrieved 7 June 2015. Jump up ^ Muramatsu, Kevin ( 2015 ). `` The State of the AR Industry ''. In Jerry Lee. Gun Digest 2016. Iola, Wisconsin : F + W Media, Inc. p. 41. ISBN 978 - 1 - 4402 - 4430 - 8. Jump up ^ Jenzen - Jones, N.R. ; Spleeters, Damien ( 31 August 2015 ). Identifying & Tracing the FN Herstal FAL Rifle : Documenting signs of diversion in Syria and beyond. Australia : Armament Research Services Pty. Ltd. p. 16. ISBN 978 - 0 - 9924624 - 6 - 8. Jump up ^ `` 27 CFR 478.11 : DEFINITION OF FIREARM FRAME OR RECEIVER ''. ATF. 2008. Retrieved 16 September 2016. ^ Jump up to : Horwitz, Sari ( May 13, 2014 ). `` ' Unfinished receivers, ' a gun part that is sold separately, lets some get around the law ''. Washington Post. Retrieved 5 September 2016. Jump up ^ Stanton, Sam ; Walsh, Denny ( December 19, 2015 ). `` California black market surges for ' ghost guns ' ''. Sacramento Bee. Retrieved 5 September 2016. Firearm accessories mounting standards Receiver mounts Weaver Picatinny NATO Dovetail rail Warsaw Pact rail Handguard mounts Weaver Picatinny NATO RIS UIT Keyhole ( Accuracy International ) KeyMod M - LOK Scope mounts Ring mounts ( 1 inch, 30 mm, 34 mm, etc. ) Traditional LM rail Zeiss ZM / VM rail Swarovski SR rail Schmidt & Bender Convex rail Bipod mounts Swivel stud, Picatinny, Versa Pod Sling mounts Swivel stud, Snap hooks, QD / Flush cup Retrieved from `` https://en.wikipedia.org/w/index.php?title=Receiver_(firearms)&oldid=804816184 '' Categories : Firearm components Talk Contents About Wikipedia Български Bahasa Indonesia Italiano Latviešu Lietuvių Norsk Русский தமிழ் Українська 中文 Edit links This page was last edited on 11 October 2017, at 09 : 53. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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Question: what part of an ar 15 has the serial number
Answer: lower assembly