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’ve watched a couple of that guy’s videos and have found that in general he had no idea what the fuck he’s talking about at any given time. He seems to just read Wikipedia or forum posts on camera and then fills in any missing gaps with guesswork. Not sure what his credentials are or background is in, but I’d be wary about trusting it as a source of dependable historical knowledge.

KAC RIS were early issue, later would be KAC RAS.

CD

I got mine in from AU today. Both levers are the same size (despite description saying one is a short lever, so definitely go by the picture). No "F" mark. No cage code. Both arms stamped with "S" so Schmid-made for Colt is my guess. I will keep it for my Mod H build, but AU gonna AU.

I got mine today.  Pretty annoyed to be honest.  I sent them an email but do not have high hopes.

It's never not been a dice roll with those guys. Every time I order from them I have to have a backup use plan for whatever I'm getting to be safe, as it's usually not worth the hassle to return lower cost items.

ETA: Let us know what they say though, if only for the laughs.

Brownell's sometimes sells the short lever, but it is around $33, so more than the $50 for the whole Colt set from them with the set from AU.

They offered a refund free of charge.  Going to just hang on to it and hope I can source the lever by itself.

Kicking myself for selling my hotdog semi ambi a week or so ago.  Had the lever I now need.

EDIT:  They also said the current semi ambis on their site only come with 2 long levers.

The levers aren't interchangeable. It's not just a longer lever, it's a completely different safety.

Not F marked but has cage code on both levers.
Edit- purchased from Brownells early 2019

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So I’ve got a mk12 gas block on the way, and my colt barrel has not been dimpled. Should I not worry and instal? Or should I dimple? Clone correct is obviously dimpled. If I dimple, which I would like to do, is it worth buying the brd dimple jig? Or does anyone have a dimple jig for mk12 pattern gb’s that I could borrow? (I’d pay shipping and throw in something for the favor). Or does anyone have any tricks for dimpling I can use that would bypass a jig without bubba’ing up my new barrel? Any help is appreciated. I’m not going to pin it, just want to dimple it for the set screws. Thanks in advance.

That sucks about the au safeties. Did anyone post a pic of it uninstalled outside the package? Mainly the lever.

It’s definitely worth buying the SLR dimple jig for $31.99, you’ll pay half that in shipping to borrow.

I will grab a few this evening.

I've often wondered where some of this misinfo comes from? It doesn't take much to cross reference or ask someone that is in the know, yet I frequently come across questionable info published on sites by so called authorities on weapons systems.

Nice. I was looking at the brd dimple jig for $55. $30 isn't too bad even if I only dimple two barrels. I'll probably have future use for it as well, just wasn't sure if it was enough to justify buying one.

You can buy a dimpling jig.

I used one on a Colt barrel and used the specified MK12 drill size and for depth, I used the specified MK12 depth by putting a set screw drill stop on the drill and gaging it with a feeler gage.

Make sure the dimple jig has the correct spacing for the MK12 gas block.

What I did was set the bare drill through the jig and allowed the point to rest on the undrilled barrel.

I then fitted the drill stop to the drill and gapped it on top of the jig with a feeler gage.

Dimple spacing is 0.400".

Drill size / dimple diameter is 0.188". (Jig calls for 5/32" drill.)

Dimple depth is 0.115".

Instructions PDF.

https://www.badgerordnance.com/media/bo_media/249-30.pdf

@Dyzastr

People make assumptions and stop there.

Guys in this group thought the 14.5" RIS II URG had a SOCOM barrel when they only used regular M4 barrels with the FSB removed. This was before the stripped FN SOCOM barrel came out. This was simply because an article said all new M4A1s had SOCOM barrels.

A bunch of people got duped by AU just now over the ambi safety.

It's not getting duped if you willingly buy from AU.

Thank you. I'm curious how different they are. Here are a few for anyone wanting to see what the FA ambi short lever lever looks like/ how it interfaces with the safety. 1kw91 and 13629
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I was mainly trying to decide if the jig was worth getting for only a few barrels. Good tips for dimple depth. What is the mk12 specified depth?

If that's the one from AU, It appears the short lever will work from your picture. It appears to have the notches and all. I'm curious to see if they are interchangeable or not. That would be crappy if they were totally different. Can you take a pick with the ambi lever off and by itself?

I edited my post to include the dimensions and a PDF download with instructions.

I think I bought a cheaper KAK dimpling jig and besides its lower price, I got it on sale for even less.

Oh I think I bought a KAW Valley dimpling jig.

Whichever cheap one that had 0.400".

This one I think.

https://www.righttobear.com/Kaw-Valley-Dimpling-Jig-750-p/kvp-dimpling-jig-.750.htm

A 5/32" spotting drill is best to use.

Depth is 0.115".

The MK12 instructions call for 0.188" drill, which is larger (3/16"), but the jigs call for a 5/32".

This jig comes with an 11/64" spotting drill, but doesn't have the correct spacing.

https://www.youtube.com/watch?v=oyXIAlMNs9E

I have a Colt ambi SA version with a short lever. I will see if they are interchangeable.

I have an FN ambi semi-auto with the short lever and I think they do fit the select fire selector.

Thank you. I didn't catch that the BRD jig didn't have .400 til you pointed it out. Good catch.

Thanks.
Ya, the pics posted by mdavis look identical to usgi ambi's, minus the short throw.

That stinks about the AU selectors. I bought 3 of them and they are showing that they will be delivered tomorrow. The 3 were intended to replace colt semi-auto ambi hotdog selectors. I'm undecided on returning them or just using the short lever from the existing safeties on the full auto.

I just wanted the hotdogs out of my life and then AU gunna do AU. I've lucked out on larger AU "bets", but seem to be getting eaten alive and taken on the smaller purchases.

Looping in @Dyzastr on this too. While it might be because the AU safety is FA and the one I have with a short (cage code) lever is SA, you cannot swap the removable lever side. The notches on the short lever on the SA model have one fat side and one skinny side. On the FA version from AU, both notches are skinny. Go figure.

The new FN selectors at Primary Arms have long levers on the select fire one and one short lever on the semi-auto one.

The parts look like they interchange with the Colt parts.

They don't.

Yeah but they are also hotdogs on the thumb side (right handed shooter) per the website picture.

It's a full blown conspiracy now.

Here's a Brownells colt FA safety short lever. unopened in bag still.





Thick and skinny on the short lever, and a shot looking down the barrel which matches - short and skinny.

I can go dig up the spare semi auto colt ambi selectors i have to confirm if they are the same, but for some reason i think they are, one thicc and one skinny.

Maybe a subcontractor variance? who knows.

Good point. Could be a subcontractor (or Schmid) variance? Here's another picture I just grabbed. From left to right: 1) AU Colt (?) FA Ambi, no cage code, both levers marked "S", notches are same width, 2) Colt SA Ambi, "S" long and "13629" short, notches differ in width, 3) Specialized Armament SA Ambi, no cage code, both levers marked "S", notches are same width.

Who knows....

I didn’t even notice the thin/thick difference at first glance. Looks like there is zero interchangeability. Unless you wanted to put an au long ambi on a colt fa ambi. @pezboytate was right. Different designs, however they are close.

Eta- my 13629 colt and 1KW91 have matching notch configurations.

This is a complete guess, but it seems like the difference is not split SA/FA or even Ambi/Non-Ambi, but rather short arm/long arm (i.e. short-arm ambi uses different width notches while long-arm ambi uses same width notches, both regardless of SA/FA). I wouldn't think that makes for a very efficient manufacturing process, but what do I know?

Ya, I'm at a complete loss now. So are those AU's even technically colt? Or Colt contract? I'm curious to know what they are. Because the original ad stated a short came with it, but I’m guessing it wouldn’t even have worked with it if it would have come with one. The ad still shows the three diff part numbers that I assume equates to the long and short throw plus the safety.

I checked the colt part numbers in the ad prior to ordering. Long and short is what was supposed to arrive.

Another member in another thread said AU accepted the refund request without any pushback. That's what I'll be going for when they arrive tomorrow and onto the Brownells backorder we go. I'm not paying $90-110 in the EE for something that lists for $49.. and comes in stock regularly..

Probably a good reason they are willing to take em back.

I saw some of the $110 ones the other day. Same day I found the $275 four prongs. The price of instant gratification I suppose.

I'm going to keep mine. The ambi long-lever sans hotdog is actually a decent replica of the old DPMS ambi safeties that were in the SPR A1 lowers back in the day, so I will just use it on my incomplete Mod H lower. That said, fool me once with AU...but I'm sure I'll be back again. Like you said, it's the small parts that they are hit-or-miss on it seems.

No idea, but what I got from AU is a 95% match to the semi ambi safety from Specialized Armament (in my picture far right vs. far left). The only different between the two is the attachment screw and where the stamped "S" is located. My guess is both a Schmid safeties made for Colt and Specialized Armament just uses a different, lower-profile screw on their version.

FWIW, the Brownell's Colt FA selector is F marked, is long/short, and has cage codes on both sides.  The one I ordered 60 days ago came like this.  If you don't want to dick around with AU, I recommend signing up for notifications...

It's hot dog, the right side lever is wrong. I'm sure it functions as a safety but this is a clone thread, right?

Isn't that how the semi-auto Colt's are too?

I think the short levers are interchangeable between Colt and FN.

Odd that both new select fire sets have long levers.

I dunno, is it? I mean if I don't have a FA Colt lower then who cares right?

But I should have clarified. The AU is (at least) non-hotdog. The Specialized Armament is hotdog given it's semi.

To those of you that are hesitant to buy the auto selector because it's auto.

Using a full auto selector in a semi auto AR15:

If you have a semi auto trigger and semi auto disconnector and don't remove the nub from the auto selector, it will be safe semi safe.

If you have a full auto trigger and semi auto disconnector and don't remove the nub from the auto selector, it will be safe semi semi.

If you have a full auto trigger and full auto disconnector and don't remove the nub, it will be safe semi hammer follow. Depending on timing, this could result in multiple shots being fired. It's probably not a good idea to use this combo.

If you have any trigger and any disconnector and remove the nub from the auto selector, it will be safe semi semi.

If your AR15 doesn't have selector stops, the selector will be able to travel past safe while rotating counter clockwise and will be able to travel past auto when rotating clockwise.

Function check it after you install it. Make sure it goes from semi to safe with the bolt forward and locked to the rear.

Very often in 9mm blow back AR15's, you'll get more than hammer follow and possibly mag dumps, with full auto trigger parts.

I remember the early 9mm semi-auto bolts were solid on top and didn't allow a full auto hammer to be used.

In this Coast Guard pic you can see the GG&G rear sight with logo.



Another pic with what I think is a GG&G rear sight and a GG&G optic mount.

That chop saw tho.

That’s a QRP mount and ARMS #40 rear sight.

I thought the sight looked a bit different, but I couldn't quite place it.

I have seen them with GG&G optic mounts though, because they had the logo right on them.

Thank you Colt civilian engineers/designers.