When discussing the Mk 18 / CQBR program, we can divide the history and discussion in to two distinct categories: 1) The weapon system itself / upper receiver supplied and 2) the group of accessories deployed on said weapon systems (SOPMOD).

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Mk 18 Mod 0 / CQBR

The M4 carbine 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.[citation needed] 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 and the United States Navy's Explosive Ordnance Disposal (EOD) Operators.

Wikipedia has a good article with sources on the original CQBR/Mk 18 Mod 0 and its development.

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SOPMOD

The SOPMOD Program Management Office at NSWC Crane, IN, provides standardized, versatile weapons accessories to meet needs across SOF mission scenarios. These accessories increase operator survivability and lethality by enhanced weapon performance, target acquisition, signature suppression, and fire control.

The CQBR itself was originally part of the SOPMOD program as an accessory replacement upper receiver for the M4. However it was eventually separated out into its own project.

SOPMOD accessories for the M4/CQBR originally included things like the KAC RIS/RAS, SOPMOD stock, KAC M4QD suppressor, AN/PEQ-2 illuminator/laser, ECOS-N red dot, ACOG, etc

The SOPMOD program has gone through multiple minor and major evolutions throughout its lifetime. The most significant is commonly defined as "Block II" and included the introduction/replacement of accessories that met the updated needs of operators. The most visually significant "Block II" accessory is probably the replacement of the KAC rail/FSB with the  Daniel Defense RIS II free float rail with low-profile gas block. Other updates include things like the Surefire SOCOM sound suppressor, EOTech RDS (553/SU-231 & EXPS 3-0/SU-231a), LA-5/PEQ ATPIAL, etc

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Link to docs and photo albums

 Presentation on CQBR from Crane
 Operator's Manual for Mk 18 Mod 0
 SOPMOD Program Overview presentation from Crane
 Photo Album of Mk 18 Mod 0
 Photo Album of CQBR with SOPMOD Block II accessories

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Because of the long history of both the CQBR/Mk 18 and SOPMOD programs, it's common to find weapons with various mixed configurations in the field, all depending on what time and unit the weapon system belongs to. Below are a few examples with descriptions to illustrate this.


Example of a Mk 18 Mod 0 in as-issued configuration including: M16A1 surplus lower receiver, SOPMOD buttstock, KAC RIS, KAC M4QD flash hider, Aimpoint Comp M2 in Wilcox mount, LMT rear fixed sight, CQD rear sling plate.


NSW Operator CQBRs with original SOPMOD accessories including KAC M4QD sound suppressor and AN/PEQ-2 IR Illuminator/Laser.


Member of a Combat Camera team with a CQBR with KAC RAS and M4QD flash hider but with other updated accessories from the "Block II" SOPMOD kit including SU-231a (EOTech EXPS 3-0), EOTech G33 Magnifier, LA-5/PEQ ATPIAL, Insight WMX-200.


Good example of "early" CQBR with SOPMOD Block II accessories including SU-231 (EOTech 553) and SU-233 (Insight M3x weaponlight).


Example of a more "modern" CQBR with SOPMOD Block II accessories including the updated SU-231a (EOTech EXPS 3-0) and Insight WMX-200 weaponlight.


Many times certain configurations are common within certain branches/groups. Here a Marine Raider is seen with a CQBR with an AN/PEQ-16 (USMC issued vs. the LA-5/PEQ SOCOM issued ATPIAL) and KAC NT4 suppressor (vs. the current Surefire SOCOM suppressor).

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Building a clone

If you're interested in building a "clone" of a Mk 18 or CQBR equipped M4A1, here is a basic parts list to use as a guide and get you started. This list is not exhaustive and see the * note above regarding personalized accessories.

                       | Mk 18 Mod 0                      | M4A1 CQBR Block I                   | M4A1 CQBR Block II                                      
Lower Receiver         | Mil-spec forged A1               | Mil-spec forged A2                  | Mil-spec forged A2                                      
Stock                  | Gen 1 SOPMOD (Black)             | M4, CAR, SOPMOD, CTR & others       | M4, CAR, SOPMOD, CTR & others                            
Pistol Grip            | A1                               | A2, ERGO & others                   | A2, ERGO & others                                        
Rear Sling Plate       | CQD                              | CQD                                 | CQD                                                      
Upper Receiver         | Mil-spec forged M4 profile       | Mil-spec forged M4 profile          | Mil-spec forged M4 profile                              
Barrel                 | 10.3"                            | 10.3"                               | 10.3"                                                    
Rail                   | KAC RIS                          | KAC RAS                             | DD Mk18 RIS II (FDE)                                    
Rear BUIS              | LMT Fixed                        | LMT Fixed, MATECH, & others         | MATECH, KAC 300m, & others                              
Front Sight            | A2 FSB                           | A2 FSB                              | KAC 99051 BUIS (Taupe)                                  
Front Sling Attachment | FSB Sling Swivel                 | FSB Sling Swivel                    | CQD                                                      
Muzzle Device          | KAC M4QD                         | KAC M4QD                            | SureFire FH-556-RC                                      
Supressor              | None                             | KAC QDSS NT4                        | SureFire SOCOM556-RC (FDE)                              
LAM                    | None                             | PEQ-2                               | LA-5                                                    
Weaponlight            | SureFire M962                    | SureFire M952, M962                 | Insight M3X (Tan), Insight WMX200 (Bronze)              
Optic                  | Aimpoint Comp M2 in Wilcox Mount | Aimpoint Comp M2 in QRP Mount, ACOG | EOTech 553 (Tan), EOTech EXPS3-0 (Tan), ELCAN 1-4x (FDE)

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Link to previous threads

 Previous Mk 18 / CQBR Thread Part I
 Previous Mk 18 / CQBR Thread Part II

I am learning. Thank you!

Is the Rock River Arms fixed rear sight desirable as an alternative to the LMT?

Not that I'm aware of.
That just looks like a chopped carry handle, an expensive chopped carry handle.

At $230, the L8A fits the same description.  

just chop a carry handle... that is what was originally done and you see them in photos if you look close enough.

That's the route I take.

Between $40-$60, sometimes cheaper.

That's exactly what I did with mine. Little homemade touch to it.

Thats what I was gettin at... Just chop a carry handle for cheap lol

I never was good at reading the room.

I used to have one of the lmt factory chopped rear carry sights. I sold it here for 50$.

If only I had held onto it I’d be set for an OG build.

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Anybody have a clean Wilcox Comp mount they'd be willing to part with?

Naw, but I have an LMT chopped rear BUIS that I'd trade for a fair amount of 300 blackout mags.....

Hoping to get some help here. I've put a 10.3" CQBR barrel on a 6520 upper and I can't get it to run unsuppressed. What buffer is popular with this setup?
More info here...https://www.ar15.com/forums/armory/Need-Help-with-SBR-Build-Non-Functional/51-549961/

I also have a new Colt M5 CQC upper  assy inbound for another shorty build.

Standard USGI spec is for a H2 buffer.

KAK has Contract spec 10.3 and 14.5 Socom profile barrels in stock at the moment

https://kakindustry.com/govt-contract-clone-ar-15-barrel-5-56-nato-10-3/

Thanks!

what would be the correct spec gas block for it ? badger ?

Any Scalarworks with T1/T2 ITW pics?

Made me dig out some old pics lol.
NSW dude rockin a Sw mount.
Eta: From 2021, man time flies.

Good looking rifles.

hmmmm

Been a few years since ive stuck my face in here.  Anyone have a Tan 553 laying around?

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Are the chf or button rifled?

>air force just doing air force things

Looks like a complete DD and do I spot a M33 cherry on top?

🤔

What's going on here! A full factory DD Mk18 RIS III

What branch and unit?

Got that TNVC IR Flag patch that TNVC won't sell to us plebs. Lol

17th STS

"Barrels are true mil spec to specifications per the militarys request and drawing.  Material, rifling form, chamber dimentions, chrome, finish, etc".

Like this? Nope, none around here.

Let me get that.

Nvm

@2Keylows
Who fixed your Delam'ed EXPS ?
is it old Logo or new Logo?

Pretty interesting that the upper seems to have been a RIS II DD upper that had a rail swap given how the lock up plate is a totally different ano color.

Just saw the mention.
New logo, 3/12/2019 DOM.
I reached out directly to Eotech CS. Luckily, still under warranty. 3 weeks total to get back.
@FastCar

This is true. AF be wild.

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Need an optic and a light.

Doing some drills and these are stupid light and easy to handle inside a car or vehicle.

Nice.

Even lighter if you ditch the SOPMOD stock for a CTR or CAR-15
But then it gets heavy once you add on all the accessories.

I'll have to see how balanced my Mod 1 feels once I get the can on it... Might swap back to a SOPMOD stock if it feels a lil too front heavy.

I know of a .gov entity (non-.mil) that uses these as well. I'm actually in process of building a clone that nobody here(or very few) here have ever seen.

The final piece has arrived!

Going to have to reposition my light, as it sits right now it blocks the tab on the collar

Light is fine.  You're not going to want to remove the suppressor once you realize how much you enjoy shooting it.  I appreciate your darker paint scheme.  Full blown desert isn't always the way for us Midwestern guys lol.

Pic thread, and some days I miss it.

I just rotated it to the 3 o'clock position, no big deal.

I have to share it with my M4A1 Block II clone lol
Although it'll spend WAY more time on this rifle.

Or you might be able to rotate the flash hider /mount (depending upon the style). Mine is a 4 prong SF so rotating was very simple.

If possible, can anyone PM me the font type and size of the Colt roll marks.  Thanks!

Brits
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Hot

The one clone I still need to build.  Need the darn rubber butt pad.