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

It was correct at least at one point. I can't say that all of the barrels were cut to that spec or not.

If you cut a barrel to exactly 10.3" with a .63" thread length, it will be too short. Crane cut down barrels are about 10.35" with a .60" thread length. Colt 10.3" barrels are about 10.38" with a .63" thread length. The problem is that ADCO and others don't know this and they probably don't care.

The mod 0 was an adco job, and it really appears more like a 10.5 than a 10.3. to me. The mod 1, I was told, is factory, but I have my doubts  based on the marks left on the barrel. Only a date, no c mp or 13629 which leads me to believe it's chopped. The shoulder of the barrel is even with the end of the ris ii so, I'd say it is spot on.

@milspec556 besides avoiding having to cut down a precious rail ladder, I have the sight that way for ease of access. As I was  installing it, I noticed how the design almost begs to be placed like that. It has wigs to protect the sight ears, which is useful more so when placed like that, and the under side has a recess cutout to aid in flipping the sight, which is basically lost when it's placed like a std sight. I'm not sure if there is a right way, but that works for me. I honestly thought I'd get more flack for a qd in place of Cqd or the m900. Honestly, I'm just glad to have a rail that the 99051 can feel home on. Even if it's makin room for a rail ladder.

eta- if I had to guess based on shoulder of muzzle to bayo lug distance mine is close to a 10.4(mod0).
The bottom barrel is the colt cutdown by adco (through previous owner). Note: the tan ring of paint is on the fh, not the barrel. Adds the illusion of being even longer than it really is. Need to strip it but not really bothered by it enough to do so.

All my replacement barrels that we have received from Crane for rebuilds have been Crane cut down Colt Govt profile 14.5" barrels.  Haven't received any in a year however and the last few were new FN SOCOM profile 10.3".  On leave right now so won't be able to measure for a few weeks.

CD Attached File


CD

The progression of my cqbr obsession.

I'm about to finish the Mod 0 and planned on the classic look with LMT rear sight Comp M2 with a Wilson mount.  However, I have trouble with Aimpoints.  The dot looks like a blob.  I was thinking of a TA01NSN for the Mod 0 with a Matech rear sight.  Thoughts or alternatives?  Thanks

Factory too. Not chopped by CRANE either. See this is why you should be following all the clone threads

Same here. But yeah it has always been Colt 10.3 govt, throughout the Mk18 Mod 0, Block 1 CQBR, Block 1.5, and most of the life of the Block 2/Mod 1. The FN 10.3 SOCOM is something he found this year. Pretty awesome.

Yeah the problem for us with FN is due to TDP rights their commercial products and mil products have to be manufactured at separate factories unlike Colt. Since they snagged their lions share of the last M4A1 contract they make military SOCOM 14.5s and now SOCOM 10.3s, but without sourcing "fell off the back of the truck" barrels, we are stuck with their commercial stuff. Which is a major bum deal.

Attached File

Well here is what I got so far. I know the lower is WRONG I am waiting on my stamp for my 6920 Lower. PRI CH and EXPS is on its way aswell.

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The MK18. Finally took the plunge. Hopefully the 4-Prong and Colt building block will stone for my pistol brace sins.
Haven’t had a chance to shoot it yet, but I’m in love with this build. Attached File

The early barrels were Colt barrels cut down by Crane to 10.5". As far as any LMT barrels go there is only one purchase documented for 40 10.5" barrels and there is a question as to whether any actually made it into builds or were just for testing. Once Colt was contracted to supply the short barrels the length was revised to 10.3".

I would tend to agree but everyone knows the the first barrels were Colt barrels cut down by Crane.  However based on the article I linked to the Crane cut Colt barrels were 10.5" and were revised to 10.3" only when Colt started supplying the short barrels. From this I would have to say that there were either 10.5" barrels fielded or that none of the original Crane cut barrels were fielded.

Based on the acknowledgments at the end of the article there is little doubt that these people knew what they were talking about.

Crane is still cutting down Colt barrels for use in CQBRs, that never stopped as far as I know. Crane cut down 10.3s are still being supplied currently as replacement barrels for CQBR URGs along with some FN SOCOM 10.3s that have appeared recently. I'm not 100% sure if new URGs come with cut downs or factory barrels, but Crane cut barrels are definitely still being supplied for replacements. Either way, you'd have to be cloning something very specific and very early to get away with a 10.5" being acceptable.

We've had pics here of URGs directly shipped straight from CRANE as received, brand new. Standard chopped 10.3 Colt govt.
@Combat_Diver in your supply system can you request full CQBR URG's from CRANE as well, or is it only for the individual parts that you normally order and receive?

Yeah, I thought so, but couldn't remember for sure. You'd think Colt factory 10.3s would be used in some capacity, but I've never really gone looking for that info specifically; no idea if it's all cut downs or a mix depending on availability on current CQBR URGs. Either way, Crane is still supplying chopped barrels, so there is no question that Crane cut barrels were and are currently being fielded. Just not 10.5s.

'Cept for mine, you see. My 10.5 is currently being fielded in the mountains of Arizonastan, and has been "seen in the wild" quite often. Feel free to clone away ;p.

Don't know what I'm going to use it on, but it just showed up today.

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Since you seem to have more lights than rifles I suppose you could dummy cord it to your ding ding and do the helicopter dick

Yeah, I have no idea why I've got so many lights.

Ding dong buzz saw!

Because Surefire Weaponlights are the bees knees that's why. You could grab a rifle with the most pic rail real estate and see how many surefires fit on it.

Don't temp me. Working nights, Tito's to wind down with and ambien makes me do some weird shit.

Whatever you do, just don't try to spell squirrel.

Ambien walrus makes the CQBR freaks come out at night

The walrus visited me one night and I woke up the next morning to an email welcoming me to ARF. No idea that I did it and the first thing I noticed was that my name was misspelled.

Same thing happened to me and FB. Minus the misspelled name.

That's a damn nice $75 dollar find. "I'd buy that for a dollar!"

I thought so too.

@milspec556, I think I figured out what happened to this guys handgurd mount up system. I think this is what happens when you have an ris ii mounting bracket behind the barrel nut, and try to force a dd lite rail to fit. I have an o.g. Dd lite rail, and thought I could just slip it off and install the ris ii.... Nope. They don't line up. Almost cross threaded/ stripped out the mount. The top four bolts lined up, but the bottom was off. Made me wonder if the same thing happened here, just vice versa. So I guess the lesson is, if it didn't come with the rail, don't try to mount it? Although it appears to be working for him.


Eta: I'm glad the dd lite fsp that was in the EE finally sold. I do not need another rail/ build.
eta #2: is that a sf mini on the end of his muzzle?

I'll be damned. The unanswerable has been answered. Good work.

Now we just need to get ya on the cure for cancer!

I noticed we both have a first gen m951. The one with the older mounting bracket. Mine has the sw02 tailcap, but I do have one of the tail caps that yours appears to have. I don't think I'll ever sell that one.

Cancer can wait. Workin on multiple sclerosis currently. Wife was diagnosed 4 years ago and it has (been) rough! Drs don't know what causes it and no cure in sight. Any way, one thing at a time. (The cure for cancer was vegetables all along! Momma was right to make us eat  our veggies, but terribly wrong to reward us with Micky d's!)

edit it to correct grammar

I don't even know half of what lights I've got. I see one I like, buy it, play with it for a while, then toss it in the pile.

I meant to say, I'll take that ugly beat up silver one off your hands. I'm the same way with lights.  I told myself to sell some b4 getting anymore, but that hasn't really been workin for me.
Here's the one

I'm a hoarder when it comes to shit like that.

Just found a ti-7 pic. I recently got one for a friend, and I mounted on my cqbr, and it's great. The rounded heel of the buttstock feels great when shooting heads up. I'm likin em more and more. Plus the placement of the adjustment lever is nice, and to take the stock completely off, you just pull the lever the opposite way. Easiest one I know of to remove.

Eta: check that finger placement.

I believe that is @Stukas87.

B5 Gen 1 Sopmods are back in stock at Brownells.

Ok.....flame away.....blade stays on for another 5-6 months...

Tried to find something to flame about. Couldn't find it. Cept maybe the Aimpoint.

Nice CQBR bud

Thanks milspec! I was worried due to the blade and black PEQ15....pic thread.

Chopped KAC vert grip you say? I did mine the other night, still needs some work but I like it so far. I know the rifle doesn't fit the thread so please don't flame me to hard.

Attached File

I don't know what anyone else thinks, but we've had a pretty good (and pretty rare) run of excellent first rifle pics.

Great stick, thanks for sharing!

A Black peq is better than invisible! If you squint hard, i mean really hard, till your eyes are completely closed, you'll see it. Why else would my 99051 be on backwards? The guy I bought it from said its Fde, but I honestly can't tell. And I didn't realize the invisible ones cost almost twice as much as a visible one. Somethin to do with extremely limited runs.

I have tried searching high and low for some rough numbers here for a comparison I'm doing but strangely found nothing. So, could a couple of you chime in with your rough unloaded weights of your Mk18 CQBR rifles that are fully outfitted with optics, IR laser, suppressor, etc.? I realize there are an infinite number of variables here, but I'm looking for a rough approximation. Thanks!

That's where your finger goes when you shoot

Don't even sweat it bro. I've seen everything in use from black PEQs to black surefires, EXPS, 553. You are good my man.

@SecretSquirell and @DontBuryMe the wait is finally over, my baby is home
Its not often at all MILSPEC gets a new gun so needed to share it with my CQBR brethren