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 do boff. I'll probably never get rid of the CQBR.

Edit: Got to add a pic for page ownage.



And the CQBR:

That's not all carbon build up in those pictures; there is some actual blast erosion as well. There is carbon, yes... but it's also already cutting into the blast baffle; mine is doing it with less than 1k on it. Of course, it's purely cosmetic at this point, being the blast-baffle is like 1/8"-3/16" thick, but there is definitely some erosion already. If I hold it at an angle it's very easy to see minor cuts spiralling outwards from the bore - the pictures only show it slightly.

Here are some better pics:





If you look at the bottom "tine," you can pretty clearly see where it has cut into the blast-baffle and the step down from the height of the surrounding surface. The same is happening on each "tine," the photos just don't capture it very well.

As to whether a 3P or 4P wears faster, I doubt there is a significant difference; certainly nothing like the difference in an MB and flash hider. There might be some merit to the notion that the blast is split into four points of impact versus three, and that serves to disperse the blast to some degree, but I doubt it'd be anything major. Either way, clearly the RC was designed for the 4P (as I recall, SF came out with the 3P for commercial use after they had already secured the SOCOM contract using the 4P/RC). Only seems right to use the MD it was designed for.

ETA nvm. I just brain farted

#DroopyBUIS

Lol... yeah, the index point would stay the same ;p.

In before krdt turns his BAFFLES 2 degrees to the left

(You can't tell me you at least hadn't thought about it)

*Turns on the welder and angle grinder*

I'm sure there is absolutely no way this could go wrong :D.

Damn you caught me before I edited right to left. Its just one of those days. Firing on 7/8

I took some quick pics of my "virgin" RC and RC2. You can also kind of see some carbon buildup on the RC1's mating surface. The oil residue is from the CLP I used to clean out the carbon.

RC:


RC2:


I spray painted the RC2; it's originally black.

Damn you did a good job with the rattle can

I'll hit you with some tomorrow as soon as I throw on my FH.

I'll send them via IM as to not angry the 10.3 CQBR gods.

Unless the rest of you heathens wanna see.....

7 out of 8?? Giving yourself some credit there!

I didn't know you were a v8 to begin with anyway.

Of course. Inline 4 the 2 wheels (unless dirt bike then single cyl obviously), and ya V8 anything with 4 wheels. That's just how it goes.

Looks like I will have a new piece for my CQBR here soon. One I've been bitching about wanting for months now....unfortunately no it is not a new optic

Mine wasn't so pristine unfired :\.



Kinda had some oxidation - I'd guess it sat in some warehouse for quite a while, then a year in jail. I also didn't realize the RC2 had a different baffle design. Have you fired them both to see how they compare with back pressure?

Also, fantastic job on the paint there. What colors did you use?

Thanks! I can't wait to wear it in after putting some rounds through it

I haven't used either yet, but hopefully will have time soon.

I believe the paint I used was Valspar flat indoor/outdoor spray paint. The code on it says "84230 Rugged" and that's on the suppressor body. I also remember spraying a dust coat of Valspar Frosting "66504 Frost" to help take away any shiny highlights/reflections from light. For the collar I used some 20+ year old automotive solid gold (no flakes, almost 24k plating looking) spray paint, and dusted over with Rustoleum 7274 Antique Brass Metallic followed by the frosting. I was hoping I'd get the tanodized look. It would have looked sort of close to the RC1 in my picture, but the RC1's collar was saturated with oil and/or finger prints so it looks kind of dark. I only had the tan SF Warden to go off of while the RC1 was in jail. A lot of work only for it to burn off I know

Note: I've used this spray frost to also flatten out satin (semi-gloss) paints on one of my rifles because the Lowe's by my house doesn't have a wide range of flat paints, but they have some nicer colors in satin.

ya, I can definitely see the wear in that pic. I think we are saying the same thing pretty much. when I spoke of erosion, I should've been more specific and said bore erosion vs baffle erosion vs port erosion. the little ports aren't nearly as important on accuracy as the bore. if the bore looks the same on both then they are fine. like you said the ports act as another escape route for gas, similar to having a larger blast chamber. im sure the gas is going to find its way through there one way or another. I guess my main point is that I believe the 4 prong was developed and chosen because of its flash hiding capabilities with NV over it lining up with. Put a 3 prong on and you now have an open vertical slot that could send flash into view. the four prong however, has an extra tine to mitigate flash as well as offset slots that direct any flash away from the line of sight. Now I have to wonder, why in the hell did they even released the 3p? I guess I had two main questions that kind of blurred. 1) are the 3p and 4p any different when it comes to baffle wear i.e. which one wears less, and 2) is one or the other better at mitigating back pressure (in reference to milspec comparing a 3p to oversized gas ports.) Now I guess a 3rd) why did they make the 3p at all? i must say though, its more pleasing to see four lines of erosion lining up to four holes, than the 3/4 thing with the 3p. Our brains and eyes strive for uniformity. Either way when all is said and done, 4p+rc=pure greatness. Thanks for all the pics man.

I hadn't really thought about one of the three openings on the 3P being timed upwards, and how that might interact with NV. Overall, I have to admit I find the 3P to be a slightly better muzzle device. Phrasing is key; I don't think it's necessarily the best suppressor mount, but as a standalone MD, the 3P has less "tuning fork" ring, the tines are naturally stronger being three thicker prongs than four thinner prongs; and, while I haven't done a side by side comparison, I think the 3P is slightly superior at flash suppression oddly enough.

I do seem to recall that SOCOM specifically requested a four prong device, so maybe Surefire already had the 3P at the time, but it didn't meet the requirements of SOCOM? I was always under the impression Surefire had secured the contract with the 4P and RC, and only later developed the 3P and later the RC2. I still don't quite understand why they opted to sell the RC commercially, but not offer the 4P when they were clearly designed to work together. The 3P makes more sense with the RC2, but that still doesn't explain the refusal to offer the 4P when they were already manufacturing it for contract purposes.

I also wonder why they decided to eliminate the blast baffle ports on the RC2; did that weaken the blast baffle and cause a need to re-core sooner? As far as I know, the primary concern with suppressor wear is the blast baffle eroding (probably outwards from the bore) and exposing the baffle stack to wear - at which point you'd need to re-core.

ETA: I wonder if anyone has ever taken a photo of an RC that needed a re-core? Not from a baffle strike, but one that had reached a point that sound suppression had been meaningfully impacted and it required replacement. I'd be curious to see what it looked like and to know the round count. I'm expecting a useful life of at least 25k to 30k (or more). Based on the round counts of other RC users that still have a usable can, I think that's a fairly reasonable estimate.

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Did you build this? Looking to build a mk18 myself and what ya have here is what I plan to model my build off of lol.

Built off a chopped 6920 oem 2 upper

Paint looks good. What did you use?
NM, I see you answered already. But can't find any online.

@Combat_Diver

CD, I did go for that handstop (Ergo) in the end. Nicest one I tried so far (and a must on a pistol anyways)


Mk18 pistol and Friends by SoloDallas, on Flickr

Rustoliem khaki, forest green and earth brown

eta I thought you asked me my bad lol

Soon. Soon I will be a member of the mile high club. Lift kit on my rig so to speak.

Take it to the next bevel bruh

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@SoloDallas

Looks good, hope you enjoy it.

CD

LOL

YesSir, thank you Sir (and you stay safe, CD)

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Need MOAR Riser!!!  Not high enough...

pic...

I like this one, I don't know why, but I like this pic.

Looks very good. I like the meat hook for sure. My lgs always has those in stock. They look like they do a good job for what they are intended.

. En route as we speak.

They truly do in fact, and I was surprised that I had never seen them before until CD showed a picture of one (or more) of his builds for .mils in his shop; it was right there.

It triggered me to know more; CD didn't remember the name of that contraption but google did. Cheap, bought and installed.

Looks great, functions great. Done.

ETA: keep in mind, it's a MUST for me because California and pistol. If I could go differently, that would be an SBR and that handstop would become a VG. I love VGs

Wilco!

CD

cue cypress hill's "hits from the bong"....

looks like you could almost shoot from the hip and still get a nice sight picture.

here is one valid reason for mismatched lowers and uppers. too many uppers, too few sbr'd lowers. Also with issued guns, it depends which upper they had on the lower when painted. you'll either end up with 1 painted upper, 1 not, or 1 painted, 1 partial, or one that matches the lower and one thats is a little "off." At least thats what happens to me.



eta- my whore lower. she don't care whats upper.

What a whore... she'll let anyone anything get on top of her :\.

I dont see a problem

She is a lower of the evening... a lower with low moral fiber... a loose lower... a lower of ill repute... a scarlet lower... a harlot, a tart, a hussy!

I need a lower like that!!

@Dyzastr maybe save some parts for the rest of us man..

Not making any promises . Right now I'm on a bit of a parts purge as I build up another cqbr block1. Got a 2 moa comp m3/ m68 that needs a rifle. I'm tellin ya, the m3 is where it's at. 2moa dot (nice for magnifying) and better on batteries than the m2 (not like they ever die anyway, just nice to know.)  I'm sellin off some lights, stocks small parts etc... I don't really need anything else to finish the block one except a colt handgaurd retainer, oh, and time. And an nt4. Then I'll be set. Gonna cannibalize a b2 for the cause.

She's down for anything upper! (better said out loud) Now I just need something to silencer. Get it.

Told ya :D.

M3 is where the win lives. You've now joined the super-secret M3-instead-of-M2 Club. And the first rule of M3 Club...