Editing Close Quarters Battle Receiver (section)

{{Use dmy dates|date=June 2017}}
{{Infobox weapon
| name               = Close Quarter Battle Receiver
| image              = M4A1-CQBR.png
| image_size         = 300
| caption            = Top: An M4A1 with SOPMOD Block 1 package, including Rail Interface System and Trijicon 4× ACOG. The barrel length is {{convert|14.5|in|mm|0}}.<br />Bottom: An M4A1 with a Close Quarter Battle Receiver. The barrel length is {{convert|10.3|in|mm|0}}.
| origin             = United States
| type               = [[Carbine]]
<!-- Type selection -->| is_ranged          = Yes
<!-- Service history -->| service            = 2000–present
| used_by            = See ''[[M4 carbine#Users|M4 Carbine users]]''
| wars               = [[War in Afghanistan (2001–present)|War in Afghanistan]]<br />[[Iraq War]]
<!-- Production history -->| designer           = [[Colt Defense]] <br> [[Daniel Defense]]<ref name="Daniel Defense sell page">{{cite web | url=https://danieldefense.com/mk18-sbr.html | title=MK18 |website=Daniel Defense |archive-url=https://web.archive.org/web/20210414072636/https://danieldefense.com/mk18-sbr.html |archive-date=14 April 2021 }}</ref>
| design_date        = 1999<ref name=SmallArmsReview>{{Cite web|url=https://smallarmsreview.com/u-s-navy-mk18-mod-o-custom-close-quarter-combat-weapon-for-the-seafaring-service/|title=U.S. NAVY MK18 MOD O CUSTOM CLOSE QUARTER COMBAT WEAPON FOR THE SEAFARING SERVICE - Small Arms Review|date=5 April 2008}}</ref>
| manufacturer       = 
| production_date    = 2000–present<ref name=DanielDefense>{{Cite web|url=https://danieldefense.com/socom-mk18.html|title=SOCOM-MK18 Complete Rifle|date=13 September 2023|website=danieldefense.com}}</ref>
| number             =  10,000+
| variants           = <!-- General specifications -->
| spec_label         = CQBR
| weight             = {{convert|2.72|kg|lb|2|abbr=on}}
| length             = {{convert|762|mm|in|abbr=on}} stock extended<br />{{convert|679.4|mm|in|abbr=on}} stock collapsed
| part_length        = {{convert|262|mm|abbr=on|1}}
| crew               = <!-- Ranged weapon specifications -->
| cartridge          = [[5.56×45mm NATO]]
| action             = [[Gas-operated]], [[Closed bolt|closed]] [[rotating bolt]], [[Direct impingement#Stoner bolt and carrier piston system|Stoner bolt and carrier piston]]
| rate               = 700–950 round/min cyclic
| velocity           = {{convert|2585|ft/s|m/s|0|abbr=on}}<ref name="ndia 2003 specs">{{cite web |last1=Johnson |first1=Jeff |title=– CQB Receiver – M4A1 Carbine with 10-Inch Upper Receiver |url=https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2003/smallarms/john.ppt |website=NDIA |publisher=NSWC |access-date=22 June 2022 |archive-url=https://web.archive.org/web/20220622211731/https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2003/smallarms/john.ppt |archive-date=22 June 2022 |location=2003 Joint Services Small Arms Section Annual Symposium, Exhibition, Firing Demonstration & Plant tour |date=14 May 2003}}</ref>
| range              = {{convert|300|m|yd|0|abbr=on}}
| feed               = 20- or 30-round detachable [[STANAG]] magazine
| sights             = [[Iron sight]]s and various SOPMOD sights
}}

The '''Close Quarter Battle Receiver''' ('''CQBR''')<ref name="nswc name, savings">{{cite web |title=NSWC CRANE SAVES $970K FOR NAVSEA SMALL ARMS OFFICE |url=https://www.dau.edu/library/defense-atl/DATLFiles/2008_11_12/acq_nd08.pdf |website=Defense Acquisition University |publisher=US Navy |access-date=22 June 2022 |archive-url=https://web.archive.org/web/20220622211249/https://www.dau.edu/library/defense-atl/DATLFiles/2008_11_12/acq_nd08.pdf |archive-date=22 June 2022 |pages=85–86 |date=22 August 2008}}</ref> is a replacement [[Receiver (firearms)|upper receiver]] for the [[M4 carbine|M4A1 carbine]] developed by the [[US Navy]].

The CQBR features a {{convert|10.3|in|mm|0|abbr=on}} length [[Gun barrel|barrel]] (similar to the [[CAR-15|Colt Commando]] short-barreled M16 variants of the past) which makes the weapon significantly more compact, thus making it easier to use in, and around, vehicles and in tight, confined spaces. The overall length of the upper receiver is {{convert|19.25|in|mm|0|abbr=on}}. With the stock collapsed, the overall length of the weapon is {{convert|26.75|in|mm|0|abbr=on}}. Those created as complete rifles (rather than only upper receivers) are type designated as '''Mk 18 MOD 0/1'''. 

[[Special forces]] units utilize the CQBR for scenarios such as [[Executive protection|VIP protection]], [[urban warfare]], and other [[Close Quarters Battle|close quarters battle]] (CQB) situations.

Its former preliminary [[National Stock Number]] (NSN) had been 1005-LL-L99-5996. A complete CQBR-equipped carbine now has the NSN 1005-01-527-2288.