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

All of the "SOCOM" labeled DD Mk18 uppers should be .070, but you could confirm that with DD. Popping the block to measure is the only way to be 100% sure without shooting it. If it's the old .080+ port, you should be able to tell pretty quickly just by how it behaves when shooting.

ETA: Top o' the page. Came across these the other day that I took while painting the NQR Mod 0 (NQR as in Not Quite Right).

All the supplies necessary for a proper rattle can job: parts, paint and single malt scotch.












And a little more current:

Good to know, I was hoping that would be the case!  Would rather not have to pop off the GB.  I’ll give DD a call tomorrow.  Thank you!

I spoke to DD last month.  They said all 10.3 produced
After June or July are .070.

A little frustrated my September purchased Upper has an inspection date of March...anyway, back to regularly scheduled programming.

Pin gauge it. If it doesn't check out, get one of those gas port shrink inserts krdt talks about, or you could do it big and swap her out for a Colt barrel.

The .082 can be tamed tho. Back in the day dudes in this thread were taming them with Govnah adjustable blocks (no longer made) and H3 buffers. So you still got options regardless

My Mk18 SOCOM URG was purchased in late April 2017 with an inspection date of 4/20/17 and it's .070. I know a few others ordered them around the same period and they were .070 as well. I think all SOCOM URGs are .070.

You could always test with a few different buffers to get an idea. I had a 10.5" a few years ago with a massive gas port that ran with a H3 unsuppressed.

That current paint looks awesome. But your block2 told me to tell you she wants that paint job too. Said she feels left out.

That’s promising!

And good point, MILSPEC

My CQBR is still calling you late at night behind my back? SHE PROMISED! Now definitely no paint for that two timer :\.

I did get her a new black SBM4 brace, though. Thing is awesome; it's like the SOPMOD of braces. Unfortunately the APF tube I ordered for it won't be here until tomorrow or Tuesday, so I haven't had a chance to shoot with it. With the talk going around about individual wait times going back up and forms disappearing into FBI background check limbo for months, it gave me a good excuse to get a more comfy brace until the F1 comes in. Plus, now I can run a TD stubby without worrying about whether 26" OAL is measured via brace or buffer tube; the APF tube should put me well over 26" OAL :D.

We only had 153 1 night stands......don't punish her too much.

Speaking of SOPMOD of pistols, I have this cheek saddle I've been considering throwing on my shockwave. Literally the exact setup
(Bottom gun shows it best)

That my friend, is SOPMOD of pistols.

Not half bad. I'd say do it.

It might take a bit more convincing than tha.....FUCK IT IM CONVINCED!

That's true, the saddle/Blade definitely accomplishes the look the best, but you're still stuck with the little thin Blade jamming into areas that it might "incidentally" touch. If that sucker catches you in the collarbone it can smart. It tends to slip out of position for me as well, especially with a PC. I'm also not sure if that falls into the realm of "modifying", but it admittedly does look pretty spiffy.

I was mostly referring to the comfort and cheek weld of the SBM4 rather than it remotely looking like a SOPMOD. Although, if you look at an SBM4 from the top, it does have a profile that is similar. I wasn't really expecting that and was pleasantly surprised how nice the cheek weld is.

And now you're just spreading malicious rumors and sordid gossip about a good, upright and moral CQBR. I won't have it :\.

Lookin' good. Lookin' sweet.



What tan is that? Might have to scoop some.

I know you're upset I rammed my shockwave in your CQBR's cheeks piece, which is understandable. But to pretend she's not the dirty little slut that she is, is straight up asinine. Do you have any idea how many different loads have been shot in that thing? I mean come on lol.

At least she's not a cheap whore tho, she's pretty expensive.

As for the braces, this is the CQBR thread. We are supposed to make our guns look pretty, they don't have to actually work good, remember?

Lol. Hail to the king, baby.

It's Rustoleum Camo x2 Sand base and Earth Brown highlights.

Look, just because she has been known to swallow upwards of 300 loads in a single day doesn't mean she is a dirty slut! Well, maybe she is. At least she isn't a PAINTED WHORE like yours! HA!

Speaking of looking good, wonder what would happen if I tried to paint this SBM4 :\. I'm kinda tempted to find out.

I think our sheriff ‘s office got all the tan ones, at least they got 50 of them. The

You will like the SBM4 and APF pistol tube combo. I went that route on my clone-ish build and it is a nice setup that fits tight. No wiggle or need for tape to prevent the brace from moving.  Push it on and you're done.

And you are correct on the length...not even close to 26" to make you worry about being in any sort of gray area depending on who is operating the tape measure.

Obliterating Tan... best paint name ever lol

Got the Phase5 Hex-2 for my SBM4...now you got me wondering if I should have gone APF...

Any idea on the main difference on the APF versus a KAK? Running KAK/SBM4 currently.

Good to hear about the fit and no need for tape. I'm definitely looking forward to trying the SBM4/APF combo sometime this week; seems like it will be far more comfortable and a bit more functional than the Blade.

AFAIK the APF is the full length of the SBM4 whereas the KAK Super has a gap at the end. Maybe the APF fits tighter as well, but I don't know for sure. Basically, what influenced my choice was that the APF seems to be one of the few made specifically with the SBM4 in mind and all the reviews I found were very positive.

How do you differentiate the SOCOM labeled uppers? Mine has an inspection date of August but I don’t see SOCOM on the packaging. Hoping it’s a .70 port....

Not sure anyone but Brownells has them, but if they are available outside of Brownells they would be minus the Mk18 billboard markings on the receiver (small "Daniel Defense" logo on the left front) and the box will likely say "Custom URG". If you bought one of the DD Mk18 SOCOM URGs from Brownells then you should be good to go.

Not sure if you're referring to the "regular" KAK tube or their Super Sig, but here is a picture of the APF vs regular KAK and some measurements.  As you can see, the APF extends to the end of the SBM4. The tube was specifically designed to fit the SBM4 and has a shoulder to maintain a decent LOP.

APF/SBM4

Not sure if anyone even gives a shit but here's a weight comparison between the non rotational wmx, rotational, and clamp-on rotational.

Non rotational being the lightest.  All have batteries

Attached File


Attached File


Attached File


Attached File

Just a humble weight comparison, folks. Not showing off or anything ;p.

Okay, that is undeniably awesome, lol. Can I have one?

Sure send me PP payment k thx.

What is boils down to is non-rotational is obviously the lightest, and would prob be what I chose to run since I don't even use the rotational bodies features, I just leave it closed.

Thank you

CD

Too bad they don't have a whole line of "Obliterating" colors.

Lol that would be legit. I used to be all about the Tan Obliterating Compound. For some reason I forgot all about it til CDs pic. I think I snagged my last can on Amazon too

Can you explain the bottom one to me? Pinned flash hider or longer than standard pistol tube? it's 26" or longer right?

Humble brag or good reference info?  Thanks for posting.

That dude posted that gun in here a few years back. We all told him his shit was illegal, he pretty much said "whatever" and bounced. Then he came back 1 more time and left again. He's probably reading this as we speak.

It's whatever you want it to be lol.

Far from a humble brag, there's others *COUGH COUGH* JOHNNYSASAKI *COUGH* that would out do me in a heartbeat.

Eeekkk. Yeah it looks JUST like my setup which uses a KAK tube and Shockwave. Flash hider off, Shockwave off which don't count towards OAL anyway I'm sitting at 24" 3/4... Personally I wanna stay under 26" OAL so it can remain a pistol so I can carry it loaded in the SUV if I so choose. Just makes it easier for transporting, Coyote hunting (not having to unload between field jumps), going into war zones like Detroit etc.

I figured that his tube was not extended and was just a standard KAK setup.

There is a potentially legit ATF letter floating around in the form of an email screenshot that states you can measure OAL from the end of the brace to the end of the barrel (without a permanent muzzle device). It hasn't been confirmed through other sources, but if it turns out to be correct, that'd be perfectly legal. Lots of people are already utilizing that letter and including the brace in OAL to use a VFG. The basis for it is that ATF has already established you measure from the "extreme end" on rifles/SBRs, and those who trust the authenticity of the existing letter say it's just citing what is already established policy. Obviously rifles/SBRs aren't pistols, so I'm cautiously optimistic about it.

ETA: Granted, I'm reasonably sure if the original poster of that image did it several years ago, he certainly wasn't aware of any such potential interpretation as it's a relatively recent development. He would've been breaking the law as was generally understood at the time. Nonetheless, it looks like it could potentially be a legitimate opinion letter and braces may well count as part of OAL. It's unclear if it would be measured in "maximum possible extension" as with a stock, or simply in the configuration at the time of measurement. I would wager the latter.

Yeah it was a long time ago but I think I recall him saying the flash hider was pinned, but nobody's gonna pin/weld a Colt 10.3. Especially when all he would have to do is remove the broom handle to make it legal. (Assuming that third pin isn't even a real third pin) dude was in CA and no F/A allowed there. So who knows what's going on with that thing.

I will give him this tho, that thing looks pretty fuckin cool regardless.

I’m still mad I sold mine for $400 right before they started to sell for $700+.

That sounds sketchy as fuck.

Yeah I've heard that argument before but I'd be paranoid to run a vert grip. I run a B5 Gripstop because there is no question what it is.

Here in Michigan, the MSP Firearms Division does NOT go by Federal for measurements. Yes they agree that a flash hider unless pinned and welded does NOT count towards OAL but they want the SHORTEST firing configuration to be taken into account, even if it can only fire one round.

For example, an MK18 registered form 1 SBR with a standard buffer tube and Colt N1 Car stock would be 24 3/4 inches with the stock fully collapsed. They would consider this to be a pistol and do NOT care what the fully extended OAL is. You better register that shit as a pistol "or" have an out of state CPL/CCW also.

Another one.... The Law Tactical folding buffer adapter. Lets say you have a 10.3" upper with one of those APF buffer tubes. It's clearly over 26" OAL, its a firearm, not a pistol... Toss a Law Tactical on it and now it folds. Folded can it fire at least one round? Yes... Here in Michigan, you would then after take your measurement folded which would be under 26" OAL so it's a pistol again but where is really gets confusing is that the Feds would still say firearm so you MIGHT be OK to put a vert grip on it as that is a Federal thing.

Shit makes my brain hurt.

I suppose some people might but what a fucking waste. I know IF I pinned and welded a 10.3" with that setup I would expect people to give me shit so my second photo would be of the weld mark on flash hider just to shut people the fuck up so I didn't have to argue.

Im with you there man. Waste for sure. Which is why I also stick with the B5 grip stop and the AFG. Both of those give me a solid purchase on a Mk18 RIS II anyways so there's no need to bother with a 10.3 pin/weld. I just stick with vert grips on longer/heavier guns.

Oh, I agree; it's pretty fucking sketchy. Some guys will argue with you until they're blue in the face that it's unquestionably, unequivocally, most certainly a fact and you shouldn't even doubt the validity of it in the slightest. To me, since the letter isn't on standard ATF letterhead and doesn't come from the Firearms Technology Branch where most official opinions originate but from the Firearms Industry Programs Branch - not to mention that it's an email response with only one source for it and not a physical letter - I definitely hesitate to put too much faith in it.

ETA: That being said, I'll be rolling with a TD Stubby as soon as Fedex hurries the fuck up and delivers my APF tube. Still waiting on my SF tan tail cap and SR07, too. Stupid slow mail :\.

You got more shit than me, bitch. Lol

It's easier to just use a longer buffer tube instead of measuring from the brace. When I put my Mod 0 together, I used an Exos Defense tube and measured from bare muzzle threads to the end of the buffer tube (which I staked). Measured at 26.5 OAL with a 10.3 barrel. That's not a pistol, and I stuck the KAC VFG on it for instagram likes.

FYI - I just spoke to Daniel Defense and the guy there said, as far as he knows, all of the Socom barrels have a .071 gas port no matter when manufactured.

Really? I've always found that vert grips (held like an AFG) work better on short and light guns, and actual AFG's work better on long and heavy guns.