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Quick Look

The M4A1 CQBR was developed by the U.S. Navy in the early 2000s for close-quarters engagements. It emphasizes compactness without sacrificing the modularity of the standard M4 platform. Today, the CQBR remains a specialized choice for law enforcement, military, and SBR enthusiasts.

Why It's a Top Choice

Short-barrel design ideal for room-clearing operations
Compatible with all standard AR-15/M4 accessories
Reliable gas system balanced for short barrels
Trusted by U.S. SOCOM and naval special warfare units
Available in semi-auto lowers for civilian use

Key Variants

MK18 Mod 0

Early version used by SOCOM with Crane Receiver and Knight's RAS rail system.

MK18 Mod 1

Upgraded rail and receiver system, dominant CQBR variant across US Navy units today.

Daniel Defense MK18

Civilian-legal SBR/upper built to the same specs as the military MK18 Mod 1.

Colt M4 Commando

Classic short-barreled M4 upper used in law enforcement special units.

Brownells BRN-4 CQB

Inspired by HK416-type CQB builds with AR-compatible architecturing for civilian builds.

Competitor Comparison Table

Feature	M4A1 Cqbr	HK416C	Sig MCX Rattler
MSRP	$1,500+	$2,300+	$2,500+
Capacity	30+1	30+1	30+1
Weight	6.4 lbs	7.1 lbs	5.7 lbs
Optics-Ready	Yes	Yes	Yes
Trigger Type	Mil-spec	Enhanced	Match-grade
Notable Pro	Uses standard M4 parts	Superior operating system	Ultra-compact form factor
Notable Con	Requires NFA registration (SBR)	Heavy for short barrel option	Higher price, proprietary parts

Best Use Cases

Home defense in tight dwellings
Law enforcement tactical units
SBR collectors building clones
Professional training scenarios
Restricted competition divisions (SBR/NFA)

FAQs

What is the difference between the M4A1 CQBR and MK18?

The MK18 is the Navy designation for the CQBR upper receiver on an M4A1 lower; both are functionally similar.

Can I legally own an M4A1 CQBR?

Yes, if registered as a Short Barreled Rifle (SBR) under the NFA, or used as a pistol build where legal.

How does the M4A1 CQBR handle compared to standard M4s?

The CQBR offers faster maneuverability in tight spaces but sacrifices some velocity due to its 10.3-inch barrel.

M4A1 CQBR for Sale