Editing Close Quarters Battle Receiver

{{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.

==Background==
The [[M4 carbine]] and [[M16 rifle|M16]] are not ideally suited for all missions due to their relatively long barrels, but the modularity of AR pattern rifles allows the operator to easily replace the upper receiver. One of two proposed special mission receivers that were planned for inclusion into the [[SOPMOD]] Block II kit, the CQBR has taken off on its own. Like the proposed [[Mk 12 Special Purpose Rifle|Special Purpose Receiver]], the Close Quarters Battle Receiver has been more or less taken on by the [[Naval Surface Warfare Center Crane Division]] (often referred to as NSWC-Crane or just "Crane") as its own project following the CQBR's removal from the SOPMOD program. Just as the Special Purpose Receiver morphed into the Special Purpose Rifle, and was type-classified as [[Mk 12 Special Purpose Rifle|Mk 12 MOD 0/1]], the complete CQBR-equipped carbine has been type-classified as the '''Mk 18 MOD 0''', or the '''Mk 18 MOD 1''' with a sightless gas block and full-length accessory rail kit.

The purpose of the CQBR is to provide operators with a weapon of [[submachine gun]] size, but firing an [[intermediate cartridge]], for scenarios such as [[Executive protection|VIP protection]], [[urban warfare]], and other [[Close Quarters Battle|close quarters battle]] (CQB) situations.  The CQBR is designed to provide improvement over previous [[AR-15]]/[[M16 rifle|M16]]-type weapons in this category. The CQBR is usually issued as a complete weapon system, and not just an upper receiver. The CQBR was once only available to [[U.S. Naval Special Warfare Command|Naval Special Warfare units]] (and by extension, other [[United States special operations forces|US Special Operations Forces units]]), but the Mk 18 MOD 0 has become general issue for [[Visit, board, search, and seizure|Visit, Board, Search, and Seizure (VBSS)]] missions and, as of 2006, for [[Naval Criminal Investigative Service|NCIS]] agents deploying to active combat zones.{{Citation needed|date=August 2008}} The Mk 18 is also used by the [[United States Coast Guard|Coast Guard's]] [[Maritime Law Enforcement Specialist]]s within both [[Deployable Specialized Forces]] and [[Law Enforcement Detachments|Tactical Law Enforcement Teams]], as well as the [[Explosive ordnance disposal (United States Navy)|United States Navy's Explosive Ordnance Disposal (EOD) Operators]]. It is also used by both [[United States Marine Corps Force Reconnaissance|Marine Force Recon Teams]] and [[Critical skills operator|Critical Skills operators]] from [[United States Marine Forces Special Operations Command|MARSOC]], and is in most cases the standard weapons of choice for said operators where the range of an M4 is not necessary.

The short 10.3 in (262mm) barrel length requires special modifications to function reliably. The gas port is opened from 0.062 to 0.070 in (1.6 to 1.8mm). A one-piece McFarland gas ring replaces the three-piece gas ring set. The standard four-coil extractor spring is replaced with a [[Commercial off-the-shelf|commercial off-the-shelf (COTS)]] five-coil spring. An [[O-ring]] surrounds the extractor spring. The standard M4 flash hider has been replaced with the M4QD flash hider for suppressor compatibility.

== Ballistic performance ==
Shortening the barrel by 50% from the original {{convert|20|in|mm|0}} pattern has a dramatic effect on the velocity of [[5.56×45mm NATO]] ammunition. This has been demonstrated in studies using a Remington 700 bolt-action rifle, progressively shortened in barrel length and chronographed. With a barrel length of {{convert|20|in|mm|sigfig=2}}, the bullet travels at a velocity of {{convert|3071|ft/s|m/s|0|abbr=on}}. This is reduced to {{convert|2489|ft/s|m/s|0|abbr=on}} from a barrel length of {{convert|10|in|mm|sigfig=2}}.<ref>{{Cite web|last=Marr|first=Bill|date=2015-12-07|title=223 Remington/ 5.56mm NATO barrel length and velocity: 26 inches to 6 inches|url=https://rifleshooter.com/2015/12/223-remington-5-56mm-nato-barrel-length-and-velocity-26-inches-to-6-inches/|access-date=2021-06-29|website=rifleshooter.com|language=en-US |archive-url=https://web.archive.org/web/20211021045202/https://rifleshooter.com/2015/12/223-remington-5-56mm-nato-barrel-length-and-velocity-26-inches-to-6-inches/ |archive-date=21 October 2021}}</ref>

==Evolution==
* '''CQBR type 1''': Made from M4A1 uppers by shortening the barrels and opening gas ports, no longer produced, STD carbine buffer in use in host lowers at time of fielding.
* '''CQBR type 2''': NSWC assembled with contracted and /or overhauled parts complete with all accessories to current standards at time of build, will work with H, H2 or H3 balanced to ammo requirements:
** H works with [[5.56×45mm NATO#US Army|M193]] and [[5.56×45mm NATO#SS109/M855|M855]].
** H2 needed for [[5.56×45mm NATO#Mk 262|MK 262]], [[5.56×45mm NATO#US Navy & US Marine Corps|MK 255 R2LP]], or [[5.56×45mm NATO#US Navy & US Marine Corps|MK 311 R2LP]]; will still reliably feed and fire M193/M855.
** H3 may be needed for an extreme case, or when the gas port is eroded but the barrel still groups.
* '''CQBR type 2A''': NSWC assembled with contracted and/or overhauled parts, naked without any accessories or buffer. The buffer in the host carbine would be used or upgraded as necessary via the supply system same as type 2.
* '''CQBR type 3''': Colt-contracted upper, complete with all accessories. NO buffer supplied. The buffer in the host carbine would be used or upgraded as necessary via the supply system same as type 2.
* '''CQBR type 3A''': Colt-contracted upper, naked without any accessories or buffer supplied. The buffer in the host carbine would be used or upgraded as necessary via the supply system same as type 2.{{citation needed|date=June 2022}}
* '''MK18 type 1''': NSWC assembled carbine with contracted and/or overhauled parts complete with all accessories to current standards at time of build; will work with H or H2 and could have shipped with either. Units will balance buffer to ammo requirements:
** H okay with M193 and M855. (All shipboard MK 18s should have H buffers as this was the standard at the time of assembly.)
** H2 needed for MK 262, MK255 R2LP, or MK 311 R2LP; will still reliably run M193/M855.
** H3 may be needed for an extreme cases or when the gas port is eroded but the barrel still groups.
* '''MK18 type 2''': Colt-contracted carbine complete with all accessories (H buffer supplied). Units will balance buffer to ammo requirements same as Mk 18 type 1.
* '''MK18 MOD 0''' ('''MK18 MOD O'''): Designation given to the full rifle, consisting of CQBR upper receiver and M16A1 lower receiver
* '''MK18 MOD 1''': Similar to the changes found in the SOPMOD Block II kit, the MOD 1 features a gas block end without a front sight and a railed handguard, by [[Daniel Defense]], that extends all the way to the base of the flash hider to provide more accessory rail space for the user.
* '''MK18 [[M4 Carbine#Special Operations Peculiar Modification|URG-I]]''': The Upper Receiver Group - Improved (URG-I) features a gas block end without a front sight and a railed [[M-LOK]] handguard, by [[Geissele Automatics]]. The URG-I also replaces the MK18 MOD 1's heavier SOCOM barrel with a standard "government" profile cold hammer forged barrel with a longer gas system.<ref>{{Cite web|url=https://www.nsn-now.com/1005016713911|title=1005-01-671-3911, MODIFICATION KIT,GUN,WEAPON|website=www.nsn-now.com}}</ref> Primarily used by [[AFSOC]].<ref name="ReptileHouse">{{cite web|url=https://thereptilehouseblog.com/2021/01/20/in-the-wild-afsoc-urg-i-10-3-cqbr/|title="In The Wild: USAF SOF URG-I 10.3 CQBR"|date=January 20, 2021}}</ref>

==Specifications==
[[File:US Navy 070605-N-3642E-586 U.S. Navy SEALs (Sea, Air, Land) perform a live fire exercise for the Secretary of the Navy (SECNAV) The Honorable Dr. Donald C. Winter.jpg|thumb|right|[[United States Navy SEALs|Navy SEALs]] armed with CQBRs conduct Shoot House Training at Little Creek, Virginia in mid 2007. Each M4A1 CQBR is equipped with the [[Aimpoint CompM2]] M68 Close Combat Optic, Knight's Armament QD suppressor and AN/PEQ-2.]]
*'''Upper and lower receivers:''' The lower receiver is a standard M4A1 lower receiver, sometimes modified with the addition of a CQD RSM sling adapter plate. However, many CQBR rifles also use surplus M16A1 lower receivers. Internally, the CQBR also takes advantage of a larger gas port and modified bolt carrier and buffer assembly. The gas port has been opened to 0.070 in (1.8&nbsp;mm). A number of [[Lewis Machine and Tool Company|Lewis Machine & Tool]] 10.5" (266.7&nbsp;mm) upper receivers have also been reported to have been purchased for the CQBR program. These upper receivers feature a gas system optimized for short barrel use. The MOD 1 makes use of a forward sight delete and full-length handguard to provide more rail space for the user.
*'''Sights:''' Initially, detachable carrying handles cut down so that only the [[Iron sights|rear sight]] assembly were used. However, most of these have been replaced with the similar, commercially-made Lewis Machine & Tool fixed rear sight, as well as adjustable sights from LMT, Matech and Knights Armament.<ref name="auto">{{Cite web|url=https://clonerifles.com/cqbrblocki/|title=CQBR Block I Parts List|website=clonerifles.com}}</ref> Front sight posts are typically the standard Colt FSP. Also used are several types of reflex and magnified optics. Most commonly seen is the [[Aimpoint CompM2]] in a Wilcox Industries Corp. [[Picatinny rail|Picatinny]] (MIL-STD-1913) mount; however [[Holographic weapon sight|holographic sights]] such as the [[EOTech|Eotech]] 553/SU-231, Eotech EXPS3-0/SU-231a, and magnified sights such as the Elcan SpecterDR 1-4/SU-230 FDE w/ L3 MRDS/Docter or the addition of [[Sight magnifier|sight magnifiers]] like Eotech G33 Anodized magnifier to the aforementioned sights are common.<ref name="auto"/> On the MOD 1, the front sight is deleted and a full-length accessory rail is used; flip up iron sights may be mounted per user preferences.{{Citation needed|date=June 2022}}
*'''Stock:''' A variety of M4 retractable buttstocks are used on a standard 4-position receiver extension, including the standard "CAR" stock. The SOPMOD stock, often referred to as the "Crane stock", created by Dave Armstrong of NSWC-Crane is commonly used. The angled stock offers better cheekweld and provides two storage compartments for spare batteries. The stock must be removed from the weapon to access the storage compartments. The initial run of stocks was made by NSWC-Crane from glass fiber polymer. Because of this, they were somewhat fragile and did not always properly lock into the receiver extension. A rubber band was used to secure the latch so it would not slide out of the desired position. The current L7LA2B SOPMOD stocks are made by Lewis Machine & Tools and have none of these problems.
*'''Barrel:''' The CQBR uses a 1:7 in (178&nbsp;mm) twist M4 barrel that has been modified in length to 10.3 in (262&nbsp;mm). The diameter of the barrel under the handguards is 1.17 in (29.7&nbsp;mm). The KAC M4-QD [[flash suppressor]] is fitted, allowing use of the KAC QDSS-NT4 suppressor ([[NATO Stock Number|National Stock Number]] 1005-01-437-0324). Although it has a [[bayonet]] lug, the CQBR is not meant to be fitted with a bayonet.
*'''Handguards:''' The standard handguard for the CQBR is the [[Knight's Armament Company]] Rail Interface System (M4 Carbine RIS; National Stock Number 1005-01-416-1089), which is designed for a variety of barrel profiles and allows for the use of any MIL-STD-1913 tactical accessories such as the [[AN/PEQ-2]], [[AN/PEQ-15]], [[SureFire]] flashlights, or a [[vertical forward grip]]. MOD 1/Block II changes incorporated the Daniel Defense's MK18 RIS, NSN # 1005-01-548-1385. The current standard handguard on [[URG-I]] improved variants is a Geissele Automatics [[M-LOK]] railed system for greater compatibility with modern accessory mounting solutions at a lighter weight than previous iterations.

*'''Ammunition:''' The CQBR is designed to use standard [[5.56×45mm NATO]] 62-grain SS109/M855 FMJ and M856 Tracer ammunition. However, due to the short barrel, the heavier 77-grain Mk 262 cartridge is preferred. There are no plans to rechamber the weapon in any additional [[caliber]]s.

==See also==
* [[List of individual weapons of the U.S. Armed Forces]]
* [[List of assault rifles]]
* [[United States Army Special Forces]]

==References==
{{reflist}}

{{Commons and category|CQBR|Close Quarters Battle Receiver}}

{{ModernUSInfWeaponsNav}}
{{ArmaLite AR-10 derivatives}}
[[Category:5.56×45mm NATO assault rifles]]
[[Category:Assault rifles of the United States]]
[[Category:United States Marine Corps equipment]]
[[Category:ArmaLite AR-10 derivatives]]
[[Category:Weapons and ammunition introduced in 2000]]