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

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

https://kakindustry.com/govt-contract-clone-ar-15-barrel-5-56-nato-14-5/

Hell yea thanks. I thought I remember seeing another  Scalarworks mount rifle other than the first one you posted.

There is a bunch. It's very common.

Need to go hunt and find them. I think that's what I'm gonna run. Love the exps on black unity look but a light weight optic at 1.93 is what's most likely gonna happen. Hopefully I'll keep this one.

I have both but I like the Su233 riser more...

Barrel dated 12/2021 but yes recent supplier.

This has probably been asked but are you still working and are you still servicing 10.3's?

Yes, still working down range and ODAs have replaced the 10.3" with 11.5" URGIs, those are only on ODAs.  Still URGs within Groups just not as many.

Couple more Scalarworks on NSW rifles





I'd like to find one on a MARSOC rifle with an NT4.

I gotcha fam. Here's an OG scalarworks mount.

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and for fun another MARSOC t1 rifle that we have a bunch of pictures of but with a larue mount.

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Maybe that’s where we’re getting our Mk.18s from. All of ours appear to be Colt select fire M4 Carbine lower turned into 10.3” guns with DD RIS IIs, Aimpoint M5s on KDG push-button mounts, Magpul MBUS-Pro sights, MAWL-DAs and Surefire Scouts.

State is letting us have the nice toys here.

Pics aren't loading.

CD or LSU or anyone else, I apologize profusely if this is an amateur question, but are QR codes ever seen on Mk18 Mod 1's or is that strictly a commercial thing Colt does?

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No. They don't have hot-dog selectors, "COLT" roll marks, shaved off selector stops, engraved lettering, or 'CR' prefix serials either. Colt knows this of course, but still this is what we get.

Not on the gun like that.  Units do have a QR code sticker they sometimes stick on.

My kids MK18 clone of my MK18.

18Z50

Haven't seen any colts with em. I've seen a few FN M4a1s with a similar matrix.

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So in theory there could MAYBE, be an FN one out there remarked with 18-1. But also could be wrong. FN 18-1 below.

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Somewhat related, does any one have photos of an Engraved Colt M4a1 lower in service? I could've sworn I've seen the pics of a few before but having trouble finding em.

Thanks, looking at some lowers on GB trying to find something that would be close.

Another option is PSA M4A1 lower. Markings and font correct and “W” SN prefix. I helped PSA get that right

Standard M4A1s
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Forgot what repair I had to do to this NSW Mk18-1
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RIS vs RAS
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Another low SN M4A1 lower (started at W300000/1)  1995 yr into a CQBR/Mk18 Mod 0 as above
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As always CD you are a tremendous help, thank you!

Saving these to my phone now

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You know how many thousands of photos I have go through on my phone for these?🤪

Shorty next to Soviet ZU-23 bbl
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Very nice!

All I've seen:

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Very late production Colt.  SN is a W 7 digit and not W 6 digit where they started.  Look at my post #22 above.  Lowest SN for a M4 that I've seen was W000489.  M4's started at W000001

'20 or '21, IIRC.

What are the lowers from MARSOC typically? I know you work on a lot. Dunno if you work on MARSOC CQBR's too.

Haven’t looked at any MARSOCs since 15/16’ Then they were Colt M4A1 marked. They are in country but not in my area

That top M4A1 looks like it's 20 digits away from an M4/M4A1 that was issued to me for 5 years. It too, went through the update program.

Can these be bought anywhere?

Yup. They just have their info wrong.

https://wetworxoutfitters.com/new-picatinny-5-8-riser-mount/

You the man, thanks! Way cheaper than I was expecting.

In stock, correct and a reasonable price?

That's not how this is supposed to work

When I first got into cloning I tried assembling a complete SU-233 kit. That base riser (and the red light filter) were impossible to find back then. Someone outbid me on eBay by $500 for that mount alone. Now surplus Insights have flooded the market and those parts are everywhere. Turns out this hobby is very timing dependent.

Why the rubber?

Was missing the T pin for the receiver block and used a roll pin starter punch. Rubber band is holding it in ( bit under size)

You rule sir! Again.

Well ask and ye shall receive:

FN stripped lowers in stock

Already OOS

Like Colts, still not the same as an issued marked lower.  Everything under logo is wrong.

They were in stock for a couple hours at least

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Anyone have a line on a tanodized TA31 ECOS with fiber optic?

Pardon the holosun. Stole it off my 300 to function test the new upper and to see if I want to do a dot in Scalarworks. Ran perfect. Need to grab a T1 in Scalarworks now.

Debating whether to add a side sling swivel or RAS handguard with QD mount.

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Side sling swivel.

3 Govt uppers for lower
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