From Wikipedia, the free encyclopedia
A CQBR (bottom) in comparison to a standard M4A1 (top), showing how
the reduced
barrel
length creates a more compact rifle.
The Close Quarters Battle Receiver (CQBR) is a
replacement upper receiver for the M4A1 Carbine. The CQBR upgrades the M4 with
a barrel 10.3 in (260 mm) long, the modern equivalent of the Colt Commando short-barrel M16
variants of the past.
Its preliminary National Stock Number was 1005-LL-L99-5996;
however, a complete CQBR-equipped carbine now has the NSN
1005-01-527-2288. The overall length of the upper receiver is 19.25
inches (489 mm). With the stock retracted, the overall length of
the weapon is 26.25 inches (666 mm). The CQBR entered service in
2000.
Background
The M4 and M16 are not ideally suited for all missions, so it
was proposed that the modularity of the M16 series would allow a
user to replace the upper receiver of an existing weapon with one
more suitable to the task. 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.
The purpose of the CQBR remains to provide operators with a
weapon of submachine gun size, but firing a rifle cartridge, for scenarios such as
VIP
protection, urban warfare, and other close
quarters battle (CQB) situations. The CQBR is designed to
provide improvement over previous AR-15/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 Naval Special Warfare 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, Maritime Safety and
Security Teams, and Maritime Security Response
Team.
The short 10.3 in (262 mm) barrel length requires special
modifications to reliably function. The gas port is opened from
0.062 to 0.070 in (0.16 to 0.18 mm). 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.
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/M855.
- H2 needed for MK 262/R2LP & will run 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/M855. (all ship board MK 18’s should have H
buffers as this was the standard at the time of assembly).
- H2 needed for MK 262/ R2LP & will 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.
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 (0.18
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.
- Sights: Initially, detachable carrying handles
cut down so that only the rear sight assembly was
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.
- Stock: A variety of M4 retractable buttstocks
are used on a standard 4-position receiver extension, including the
standard "CAR" stock. Most often seen is the SOPMOD stock, often
referred to as the "Crane stock", created by Dave Armstrong of
NSWC-Crane. The angled stock offers better cheekweld as well as
providing 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 lug, the CQBR is not meant to be fitted
with any fighting blades.
- 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 infrared pointer, SureFire flashlights, or a vertical forward
grip.
- Ammunition: The CQBR is designed to use
standard 5.56x45mm
NATO 62-grain 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 calibers.
See also
References
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