The Close Quarter Battle Receiver (CQBR) is a replacement upper receiver for the M4A1 Carbine, developed by the

US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

. The CQBR features a 10.3 in (262 mm) length

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...

(similar to the

Colt Commando The Colt Automatic Rifle-15 or CAR-15 is a family of M16 rifle–based firearms marketed by Colt in the 1960s and early 1970s. However, the term "CAR-15" is most commonly associated with the Colt Commando (AKA: XM177); these select-fire carbin ...

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 19.25 inches (489 mm). With the stock retracted, the overall length of the weapon is 26.75 inches (679.4 mm). Those created as complete rifles (rather than only upper receivers) are type designated as MK 18 MOD 0/1.

Special forces Special forces and special operations forces (SOF) are military units trained to conduct special operations. NATO has defined special operations as "military activities conducted by specially designated, organized, selected, trained and equi ...

units utilize the CQBR for scenarios such as VIP protection,

urban warfare Urban warfare is combat conducted in urban areas such as towns and cities. Urban combat differs from combat in the open at both the operational and the tactical levels. Complicating factors in urban warfare include the presence of civilians a ...

, and other 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 The M4 carbine (officially Carbine, Caliber 5.56 mm, M4) is a 5.56×45mm NATO, gas-operated, magazine-fed carbine developed in the United States during the 1980s. It is a shortened version of the M16A2 assault rifle. The M4 is extensive ...

and

M16 The M16 rifle (officially designated Rifle, Caliber 5.56 mm, M16) is a family of military rifles adapted from the ArmaLite AR-15 rifle for the United States military. The original M16 rifle was a 5.56×45mm automatic rifle with a 20-roun ...

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 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 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 A submachine gun (SMG) is a magazine-fed, automatic carbine designed to fire handgun cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun, to describe its design concept as an autom ...

size, but firing an

intermediate cartridge An intermediate cartridge is a rifle/ carbine cartridge that has significantly greater power than a pistol cartridge but still has a reduced muzzle energy compared to fully powered cartridges (such as the .303 British, 7.62×54mmR, 7.92×57 ...

, for scenarios such as VIP protection,

, and other close quarters battle (CQB) situations. The CQBR is designed to provide improvement over previous

AR-15 An AR-15-style rifle is any lightweight semi-automatic rifle based on the Colt AR-15 design. The original ArmaLite AR-15 is a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design. The then Fairchild Engine and Airplane Corporation ...

-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 Naval Special Warfare units (and by extension, other US Special Operations Forces units), but the Mk 18 MOD 0 has become general issue for Visit, Board, Search, and Seizure (VBSS) missions and, as of 2006, for NCIS agents deploying to active combat zones. The Mk 18 is also used by the Coast Guard's Tactical Law Enforcement Teams and Maritime Security Response Teams and the United States Navy's Explosive Ordnance Disposal (EOD) Operators. It is also used by both Marine Force Recon Teams and Critical Skills operators from 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 (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 pattern has a dramatic effect on the velocity of 5.56x45mm NATO ammunition. With a 20" barrel, the bullet is moving at , but this drops to at 10". This has led some to question the effectiveness of the Mk 18 compared to other cartridges like 7.62×39mm or

.300 AAC Blackout The .300 AAC Blackout (designated as the 300 BLK by the SAAMI and 300 AAC Blackout by the C.I.P. or 300 AAC Blackout'' C.I.P. TDCC sheet 300 ACC Blackout/ref>), also known as 7.62×35mm, is an intermediate cartridge developed in the United Sta ...

which are not as affected by barrel length reduction.

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 okay with M193 and M855. ** H2 needed for MK 262, MK 255 R2LP, or 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. * 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.

Specifications

*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 mm). A number of Lewis Machine & Tool 10.5" (266.7 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 rear sight assembly were used. However, most of these have been replaced with the similar, commercially-made Lewis Machine & Tool adjustable rear sight. Also used are several types of reflex and magnified optics. Most commonly seen is the Aimpoint CompM2 in a Wilcox Industries Corp. Picatinny (MIL-STD-1913) mount. 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. *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 mm) twist M4 barrel that has been modified in length to 10.3 in (262 mm). The diameter of the barrel under the handguards is 1.17 in (29.7 mm). The KAC M4-QD flash suppressor is fitted, allowing use of the KAC QDSS-NT4 suppressor ( National Stock Number 1005-01-437-0324). Although it has a

bayonet A bayonet (from French ) is a knife, dagger, sword, or spike-shaped weapon designed to fit on the end of the muzzle of a rifle, musket or similar firearm, allowing it to be used as a spear-like weapon.Brayley, Martin, ''Bayonets: An Illustr ...

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 The AN/PEQ-2 Infrared Target Pointer/Illuminator/Aiming Light (ITPIAL) is a laser sight for use on rifles fitted with a Picatinny rail. It was manufactured by Insight Technology. History The AN/PEQ-2 succeeded the AN/PAQ-4C, which was designed i ...

, SureFire flashlights, or a vertical forward grip. The standard handguard has since changed to Daniel Defense's MK18 RIS, NSN # 1005-01-548-1385. *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 In guns, particularly firearms, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore matc ...

References

External links