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

Hong Kong clone of several years ago

They're still kinda hard to find though. I was more excited because it's the final piece of my build.

I was frankly excited for the price as new - first time I see it at USD140 versus the 250+ or even 300 I remember seeing it around on Gunbroker etc.
It's just a good muzzle device to have for them clones... feels good

Yeah, agreed, that too.

Good morning all,

not trying to upset the apple-cart or raise a debate, but the 10.5" LMT uppers were small unit purchases outside of the normal issued chain, right? If so, I have a couple of questions -

1) Does anyone know specifically what units/ locations purchased those uppers
2) were these kitted the same/ similar to the CQBR Blk I's as far as accessories?

Just realized the 4P can't be indexed with the tool as with the 3P; how do I tighten it? Hand tighten only?

https://www.brownells.com/gunsmith-tools-supplies/rifle-tools/wrenches/ar-15-m16-combination-wrench-prod468.aspx

That’s what I use.  Thin enough for SF muzzle devices.  I think classified defense makes a specific 4p wrench as well.

Open ended wrench/crows foot wrench/M16 wrench.

Torque value is 20-30 ft lbs.


I used a strap wrench.


If you're feeling spendy, Classified Defense sells a damn nice wrench for $35.

Got it - appreciate it, thanks!

Thanks!

(sorry about the double thanking post, saw too late)

Another technique used down range is to use the Geissle URGI barrel wrench.  Use the open hook in a tine to tighten.  Set torque wrench to 25 ft lbs (20-30)

Or get a 3/4" open end box wrench at pawn shop for $1 and put it to the bench grinder to thin it down.

Attached File

Are you a genius - CD - or what?

'cause I think you are.
Got that tool, doing now - thank you!!!!!!

ETA: done, worked like a charm - happy camper.

Thank you Sir!

I just installed mine, I used the FCD flash hider wrench.

https://www.forwardcontrolsdesign.com/jmw-joint-muzzle-device-wrench.html

Does this look close enough on alignment? It it right at 30 but it's a hair off.

Attached File

GTG

Cool, Thank you

Same tool I have used for 10 years for normal barrel nuts, flash hiders and now the SF4P.  Bought it at a gunshow 10 years ago for $10.  Sarco has it for $17.00 or $23 with taxes and shipping. Ar15/M16 Combo Wrench.

I thought the flash hiders were not timed, just thread on and go or do they need to be timed?

I don't think it needs to be timed.

That being said, if I had a son who built a MK18 and his suppressor engraving wasn't TDC I'd be severely disappointed.

OCD is a fickle bitch.

Some insist on their index tab being at BDC.

This

^I fall in that category^
Why would you want an open slot facing down anyway?

I'll take an open slot at any angle I can get it.

Oh...I think we're thinking of different things.

Whoah!

Agreed.
But you know what they say man....to each their own.

I have heard that the Vltor A5 stock was develpoed for the USMC MK18 but have yet to find a picture of one with that stock

Not quite - for the USMC M16A5, which was itself a cancelled project.

Looking for a little guidance on whether there's any utility to being able to run a Mk 18 unsuppressed.

Any of you guys, who own cans, shoot your Mk 18's unsuppressed regularly? I can opt for (A) dedicated suppressed or (B) mixed use if I have Trajectory Arms assemble my upper with their "tuning" service (BRT tube or gas block insert, tested on F/A lower).

But, to reiterate, I'm still unsure of whether there's any utility to being able to run a 10.3" upper unsuppressed.

My SOCOM556-RC2 should be out of jail any day.

All parts I have are correct (0.070" port Colt 10.3" barrel, Mk 12 gb, etc.) but the upper has never been assembled.

I shoot lefty - any marginal gas mitigation is worth it to me, even if it means sacrificing a part of the gas system that would otherwise be clone correct.

Any thoughts/opinions welcome.

It needs to run unsuppressed. Things happen. Suppressors go down. Mounts have issues. Then you are left with a single shot rifle.

Maybe try the bootleg carrier instead of that tube.

I'm in agreeance. Whether it is full time suppressed or temporarily, it needs to be able to operate with and w/o the can.

Shot mine weekly enough without a suppressor and had to rebarrel it.
Attached File



CD

Attached File

Attached File

What sling is that?

Don't know, something I picked up over there well used.  I only used it as a two point sling.  Let someone shot my rifle on the range and they let it droop over the flash hinder that sorta cut it in half (USGI).


CD

Oh, got it. I just finished my build yesterday, I need to figure out a sling.

Is there a torque spec for the kac front/rear sights and the cqd forward sling mount?

I've never seen one.


CD

Thanks, I'll just snug them down.

There are torque specs for bolt/screw diameter and pitch you can easily find with a Google search. Also thread locker is good to go.

Has anyone seen any of the FN 10.3 Socom barrels recently?

I'll take a look. I was planning on using blue loctite. Except the front sight, being it has a helicoil.

Thanks for the feedback.

Do you want the requirements for DoS mk18's here?

The what?

Help me decide between a tango down full size and a AFG-2. I have both on hand. Both are fde.