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

This is how I run mine. Works with no issues suppressed and not. Even when my gas rings broke and disappeared..

I run mine with Sprinco White Springs and a Spikes ST-T2 and it runs without issue suppressed and unsuppressed. In fact, that is the exact spring and buffer combo I use in every single gun I build. Unless it is a Rifle length tube.

I just have an H buffer with a standard spring for my unsuppressed Block II, would it be worth picking up some other weights to try out?

Probably not

Hopefully I can get to the range next weekend, I have a case of gold bars IMI coming from SGAmmo but it won't be here until Monday

The CQBR was designed to be run suppressed/unsuppresed with a standard carbine spring and H2 buffer. Try that and report back.

I threw an H1 in there with a G spring, I'll have to see if I've got a regular carbine spring, and I'll have to pick up an H2. I'll probably run by the range tomorrow to see how it runs after a good cleaning and buffer/spring swap.

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Thanks for those. That 3rd one, what a great example of blending wearable gear patterns with the environs. (Perhaps not even intentionally, but it works out great.)

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SL

Skeeters. Skeeters everywhere.
What an expensive pic man lol.

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Just saw that posted, hot!

A case of clone-fuel along with a case of '470 fuel



And a little entertainment for the evening

Anyone have the pic of the mk18s in he wild and the dudes are rockin the patagonia pcus in alpha grey?

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Badass pics but its a different one than these.

While swimming through the $.90 9mm today at the gun show I found this colt SOCOM for an amazing price
Now to flip or keep
Would go very well with my mk18 build I’m doing


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Looks like you’ve already listed it in the EE. Note that the alternate rear site you mentioned in the ad is a MaTech. I’m assuming it’s the commercial one since you called it a “Picatinny” rear sight, but that’s just a reference to the mounting type and not the brand . GLWS.

I’m using the same lower for my CQBR.

Nice, I have that Nodak m16 lower pictured that is sbr’d and another Colt M4 marked that I could sbr.
Just trying to see if it’ll sell if not I’ll shoot the piss out of it.

Mine was the same version as yours with the Troy rail.  I got lucky and snagged it for about what the lowers were selling for on their own.  Kept the lower and sold the upper.

I paid $1100 with a Geissele in it
Oops

What surefire light or mount is that?

New Surefire PRO series comes w/ built in rotational mount for mlok/ rail.

Those of you who have experience w/ the KAC skyscraper mount, how does it compare in height to a MRDS mounted on top of an ELCAN?  

Really got the itch for one and since I haven't found a MK6 to complete my ECOS-O, might as well get some use out of the MICRO.

I’ve used both, but it’s been a while so I can’t give a comparison unfortunately. I’m a big fan of the skyscraper.

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Yea came with the Surefire 640 DF. I love it Really show how much a suppressor and light at 3:00,washes out

That’s a screaming deal in these times.  That’s what I paid for mine but without a Geissele.  That was also before the panic started.

What do the lowers go for? I may just keep the upper and chop it and send to ADCO for a build.

If I recall correctly, pre panic the M4A1 marked lowers were going for around $850-$1000.

In fairness, the "Govt Property" lowers were commanding those prices pre-panic, but not so much the older SOCOM lowers with just "M4A1 Carbine." There definitely was a time they commanded super-premium prices, but their desirability dropped a good bit once the "Govt Property" lowers became a thing.

These days, who knows. It's still more desirable than a regular "M4 Carbine" lower, and those are going for pretty nosebleed prices like everything else.

I believe I paid $600 for mine from the EE

TacoTuesday
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Dude, Baja Blast is the cat’s pajamas.  I can only get it when I make a run for the border.

Mild? Really?

Lolol mayo must be spicy to him

Edit: Didn't even upgrade to the Dorito taco! What's next a 10.5 barrel?

Fire FTW. Also, that one taco looks like a nice appetizer to the actual meal

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CD

Fuck Dorito tacos.  Assheads made everyone think the shells were actual fucking Doritos and instead they're just vaguely Dorito-flavored bullshit

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Skyscraper mount and Magpul SL-K ordered... really pushing the boundaries on clone here

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I've got a PSA M4A1 lower and a PSA 10" upper kit I want to make into a poor MFs CQBR.

Only thing I'm missing is replacing the PSA cheap ass plastic handguard with a KAC.

What's my best option for a KAC clone that's a drop in equivalent?

I realize this is not a perfect Mk18 clone, but I'm poor with two kids in private school so cut me some slack!

With or without FSB on your barrel?  I would watch EE for a KAC RAS/RIS for sale and make a Mk18 Mod 0 clone.  


CD

Today's pic
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CD

@Combat_Diver

With a FSB.

It's this gun, but I've replaced the upper with an A2 upper and the stock with a milspec stock.

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I was hoping to get a KAC-style raile for less than $250. Damn near impossible to find an actual KAC for less than that. Any clones in the $100 range?