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

Prior to Dan's group buy thread, I asked about intererst in them as well because I had a guy that used to work for Spikes who was willing to get DD to make them and at the time, the minimum was 30 rails but, that guy would only have sold them as complete uppers. He was trying to get his own business going and wanted to get his name out there. He was going to use Douglas Barrels and Spike NiB BCG in the uppers but, I could only get roughly 10 people to commit at the time.

Not sure if it would have ever came to be but, this guy was pretty well connected so, never say never. Guess that dreams long gone.

I'll buy complete uppers if need be as well. I'd still be in for at least two if I had to get them as complete uppers.

I got mine a few months ago on the EE, the ad had been there for several months at $125.  Im surprised no one had bought it, brand new to.

Looks like boltcarrier.com knocked the price down on their KAC taupe front sights to $171.

Just a heads up as that's a pretty killer price.

Good one, CMS...now everyone's going to have to get clone correct Rayovac batteries.

Lol, I have the right barrel but that's about it. If I posted my 10.3" I'd get fuckin accosted to no end..

lol, big green brick batteries.  

oh how i don't miss those...

Thats a Harris 152...not ASIP/SINCGARS brick batteries...  A whole lot smaller and lighter...about the same size as an MBITR battery.

Oh I know....the Marines kept breaking my EOD guys' batteries out on mission.    They'd break their own, EOD would be nice and loan them some.....they'd break those too.  Then of course it was just because the batteries were crap, mind you.  Nothing to do with their complete disregard for other people's stuff.  

I did the trade so if anyone wants an ATPIAL-c for a killer price pm me

They're Marines. They can manage to break anything. I wasn't so lucky. I got stuck humping an ASIP with two extra batteries on top of everything else. The MBITR didn't have the range and we didn't have any other cool guy gear.

Either way...back to the pic thread!

So with all the decent priced block 2 black fsp ris rails floating around has anyone thought about trying to modify it (cut/dremel/metal work) to convert it to an mk18 ris fsp?  I know it would tske some skill and effort but I keep thinking about it.

Well, two of the lower attachment screws (one on each side) are positioned past the FSB, so it would only have the two screws toward the rear. I don't think it would be a very good idea personally, but if someone got one for $150 and was itching to try it, I guess they could.

Exactly my thoughts.  I knew the front bolt up hole would be too far forward but I think positioning a new hole on each side woukd be easier than cutting the rail down.

The cutting would be easy... there's not really anywhere to position a new hole very well though. It would be a lot of work for a fairly unrefined final product.

+1. I got mine for 150 from Brownells too. But I'm not selling mine. Evar

I tried to but your inbox is full...

Also - DBM, thanks for the LSO Grip heads up, just ordered one.

Currently looking for a 231 marked 553 in good shape if anyone has a lead on one or is willing to part with theirs.

anyone plan to do another run of the m4 labels in the near future?

Untitled by Shift_Six, on Flickr

Untitled by Shift_Six, on Flickr

Fun afternoon

Sure thing man. I picked one up too. Just in case.

How fast were they with shipping?

At 13.55 it'd be weird not to FO

I've got my order notification, but no shipping yet. I ordered on Thursday I think... whatever day I posted about them here.

So my Mod 0 was recoiling very hard. Colt 6921 URG cut to 10.5 with over 4.5 k of wolf while running a H3 buffer and standard spring. Ejection pattern with or without my suppressor was 1 o'clock.

It was time to rebuild...

Sold off the upper and had Adco chop a new 6920 URG to 10.3. They opened up the gas port. My 0.70 drill bit was loose in the port but the 0.73 drill bit would not go in. So .072? Upgraded to a G2S trigger.

Got it to the range for the first time this morning since the "rebuild".

Over 500 rounds of Wolf, fed M855, fed M193 and privi 75 gr match. Only 1 failure! 1 lone round of Wolf did not fire despite 3 hammer strikes. Ran it only suppressed today and all casings fell from 2:30 to 4 o'clock. It ran so soft my daughter who before the rebuild would only fire a few rounds went through 3 mags!

Also the old CH was treated with a gasket sealant and still had me choking on gas. I've not taken the time to put it on the new one yet. It was not a problem. Just the faintest puff...

Pardon the YHM can, someday it will be replaced with a NT4.

Dude mine is not a soft shooter either, when I get back I'm going to tinker. Anyone know the stock LMT gas port size ( sorry to bring up gas ports)... Can't even think of what buffer I'm running. Mine ejects at about 1:00 as well... Stripping mine and adding the light when I get back too... And an S3G.

I'll ask my buddy he has a lmt 10.5

.071". Tiny for a 10.5".

+1. I measured this LMT 10.5 after I got it back from getting cut to 10.3

I got .073 with a caliper, so yeh, I'd buy .071 all day long.

Mine is a .078" gas port and an H2 tamed it.

Here is a video from before the H2, when it had a standard carbine buffer, shooting M855. It was pretty jumpy. Now its much smoother.

IMG_4331 by splittiebus 66, on Flickr                

Thanks. So you guys think an H3 will smooth it out?

I give it a teeeeeeeeen!

H3 is all these typically need. The primary reason why the gas port size discussion is off base is because solely speaking recoil, you really aren't going to feel any difference between a .070 and .082 10.3" barrel...and obviously, any size in between either. They all "feel" the same.

10.3s are snappy, regardless. You want a soft shooting 10.3, an adjustable GB is your only option.

Yeah I don't need smooth... So much as to alleviate the 1:00 ejection...

H3 for sure.

Yeeeeep. A heavier buffer did in fact smooth mine out a good bit though, in addition to moving the ejection back from the 1:30 to the 3:00.

Mine with an H2 and a .070 port feels just fine, it's just lighter than my 14.5" with an H2, YMMV.

10.3s tend to be snappier in general. Certainly more so than any of my 11.5s or 14.5s.

Mind you, I shoot my 10.3s far more than any of my other rifles, so it's not like it bothers me.

And in regards to the 10.3" gas port sizes and felt recoil, I've fired .070s and .082s side by side on multiple occasions. Multiple different host rifles as well. I can never tell the difference.

Even the MicroMOA rep chimed in before that the felt difference between the two is essentially nothing. And those guys have done extensive testing with different 10.3" configurations. Even on sustained full auto, the difference between those two gas port sizes equates to essentially nothing in regards to felt recoil.

Now, MicroMOA's Govnah on .049 with a suppressed 10.3, that's hands down the most fun shooting setup you can have with a 5.56 IMO.

Can someone remind me of the benefits that the SU-230 HD has over the standard Elcan? I remember IM'ing a member on here awhile ago, and it was something to do with improved recoil resistance? I can't remember now

Allegedly it was "hardened" for the SCAR. I don't think I've seen an "HD" model in the wild, and my overrun isn't, and I've had no issues with it in the 5 years I've had it now.

That seems to be in line with what I remember hearing about them. Were they ever sold commercially?

And do you or anyone else know what what you can buy a tan Elcan MRDS mount for these days?

I think there's at least one person in the clone threads with an HD model.

i believe the HD is only referenced to the su230-a.  the only differences are a stouter azimuth adjustment bar and red loctite applied to set screws on the azimuth adjustment.

this isn't just a socom model upgrade.   all spectre DR's received this update , even civilian models.

it was an update done after testing with the scar 17.  several companies updated optics after the scar testing , nothing wholesale but improvements for recoil resistance.  eotech went with the transverse mounted battery to improve recoil resistance , it was released as the exps and xps models.

Do you have pics that illustrate how to differentiate an "HD" SU-230?

All the ones I've seen are engraved up by the SN as shown