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

@pbjunkee - I'm in. I've got the day off work tomorrow. Looks like I know what I'll be doing. Are we doing strictly 1x magnification? Or is a 3x allowed, or 4x (Acog, elcan, 1-4x variable optic)?
eta-pic
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Its the new style. Guess I’m gonna have to find a m2. They were cheap for the longest but recently have been higher in price.

4x max

ill join in when I can get better ammo, m193 and 855 aren't even worth putting my elcan back on

Anyone know if the old style/comp m2 caps will fit the new style pros?

Has it been that long? I'm down.

Now you guys run a match as I'm on my home.  Would have been nice to shoot my URG with the FN barrel.  In my limited accuracy testing out of issue ammo Mk262 Mod 1 was the most accurate but M855A1 was a close second.  Didn't have any Mk318 to test.  Those were shooting 1 and 1.5 MOA respectfully with the 3x scope at 136m.  M855 was like 4-5 MOA and that one box of old BH 100 gr for CQB was dismal at that distance.  Course designed for inhouse shooting.

CD

They do. Buy the replacement caps, buy the rubber tether, and you just saved some money.

Eta- I'm thinking they don't now. Let me check. Nope. No threads, so they won't work.

Thank you

Time to build one at home? That’s what us lowly peasants do.
I still have one box of Mk318 left but planning on saving it for a rainy day. A real rainy day, like commies dropping in the home land by parachute rainy day.

Will the older-style knobs from an M2 fit on a PRO?

Oops, didn’t refresh the page.

No one answered, so:

Will the older-style knobs from an M2 fit on a PRO?

I dremeled. It came out fine. Actually came across it for the first time in years an hour ago while going through the "miscellaneous shit" pelican.

ETA: I'd post pictures, but it's in storage.

Great. Ya, an angle grinder seemed overkill. Maybe for the initial cut. The smaller rotary tool wheel seems ideal.

No bipod, does that mean prone with a sling is ok?

For the main cuts you could use an angle grinder with cut-off wheel, band saw, reciprocating air saw or sawzall - hell, a hacksaw for that matter. Then a belt sander or Dremel with a sanding drum to smooth and shape it. I'd likely use an air reciprocating saw with a fine tooth blade for the main cuts.

As is tradition.

get the dremel out, cut off the carry handle

might as well flute the barrel while your at it

Since I just built my 10 yr old grandson his AR, his twin 7 yo sisters what one now too.  So that's the next project, one pink and other purple!  Then there's my M110 .308 build which the 80% lower is finished with M110 stock.  Still have to get another flat top upper with rifle ramps to get to replace the M4 flat top on my M16A4 clone w/ rifle extension.  Got those two other Green Mountain 18" 1:5 and 1:6 twist uppers to build.  Wife's rifle has the GM 18" 1:14 twist bbl that we traded, its a tack driver.  Then I may work on my URG pistol.  Got a feeling my pistol lower will go to one of the girls rifles right now thou.  Got a few more years before I have to start building for my 2 mo old grandson at least.

Got lots of reloading to do and some bullet casting while I'm on medical leave.  As I'm looking at the timeline might miss deer season again, dang it.  Gotta take out the grandson deer hunting.  Need to see how M855A1 works on them.  But still have to get cleared by the Army doctors before I can deploy again.

CD

Sounds expensive. Thank God for hazard pay huh? I think I remember Aero precision selling a flat top upper with no ramps (rifle/A4 upper) a few years back so you might check there but it wouldn’t have the Colt mark unfortunately. I’ve been on a handgun stint as of late so taking a break from rifles (mostly due to law changes here currently) but think I just need a stripped lower and a buffer tube assembly to finish my daughters CQBR. Maybe a Colt upper as well to do it right. And you know it is ok to retire someday.

And done.
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We'll have to add "chops carry handles in the blink of an eye" to your list of superpowers ;p. Looks good.

Got my one good eye on Aero's upper, that might be the one I swap out unless I find a Colt (stock/handguards) or FN (FN bbl/BCG).  A4 is already a arsenal mismatch  Current upper is a FN IIRC.  There is a FN rifle ramp upper that we can't us at work, urgh!  As far as retiring, still hear those damn war drums!  Eye might prevent my marching off however.  Hopefully this heals itself, if not time to spoil the grandkids.

Well done indeed, sir!

CD

Ill allow it

Prob how ill be shooting

It's from SF. Some of their kits are packaged like that.

Thank you . My powers seem to be fading though. When I was just an embryo, a mad scientist injected me with tritium. I developed the strange power to be visible in darkness. This (seemingly useless)  ability fades as the years pass and requires tritium infusions at regular intervals.
Now we just need a sidekick and some villains. This could be a terrible comic!

I wonder why colt/ usgi carry handles ( maybe all milspec handles) don't sit flush to the end of the receiver? Lmt definitely made their a2 with the profile of the upper in mind. Is there any 1 reason? Material cost savings?weight savings? To give me somethin to stare at and wonder why?

Fun fact: when tritium is absorbed into the body it is mistaken for calcium. You can imagine the damage that would do.

Glowing bones, that's great!

Yeah until you grow a third nipple out of your eyeballs and realize your bones now have a 12.5 year half life and their own radio frequency

Sure.  I played last time.  I can play again.  It’ll be interesting if I’m better or worse post heart attack/bypass.

No one answered, so:

Will the older-style knobs from an M2 fit on a PRO?

Glowing bones, eyeball nipples, and my own built in radio? Now I'm intrigued. Let's open some acog's

I couldn't really tell you; I've never owned one of the new style PROs. Just looking at it, I'd tend to say no. It appears the old style caps are much taller and require more threads than the new style. Assuming it's the same thread and size, maybe it could be made to work, but I don't know for sure.

@C6H12O6  I answered up here after checking.
If the new style of turrets  caps pop up, they won't work, but if there are threads you might have some luck. I couldn't find any pics that showed threads so I assume the caps are pop on off. As krdt says though, I'm not 100% without seein a pic with the cap off.

Ah 10-4 guys, thanks.

Maybe I’ll just have to buy one of the Primary Arms ones then or just use my old real M2 from my M4 clone. Or maybe trade a new for old one with a doctor I know.

Let the games begin:
I realized at the range that I didn't ask which target I should use. This is an 8" round. If it disqualifies me I'd be happy to shoot again.
Specs:
Xm193
10.3" colt socom
eotech 553 with 3x mag
ten rounds
sitting
this isn't my best group, this was my best group and it's the only one of 3 with all 10 shots present on paper. Probly shoulda slowed down.
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Eta-
100yd backstop straight back. 50yd to the right. Shot 3 targets with the mod 1 and 3 targets with the mod0. Had a technical difficulty with the aimpoint mount screws not bein torqued or loctited. I put it in the mount a few days ago and whoops. Forgot to torque it completely.

I have to ask, are you saying there are comp m2s with docters on them? Seems redundant. But I guess 1 is none.
Edit- I'm a moron. I reads good now.

Right? He makes it sound like it's a bad thing.

Lol nah. One of the medical doctors I work with has a PRO with the older style knobs. He wouldn’t care if he had a non-clone looking optic.

Def looks good.  May have to try my hand at it soon.

Thank you. There are some inexpensive ($35) colt carry handles goin around now. Go for it?

Measure grease ring to grease ring and subtract .224

5.524"

That's a neat range. What's all that green stuff?

I didnt mean sitting ay a bench lol

Anyone got a lead on an EOTech 551? Not crazy about this 553 on the riser. Think the 551 will look just right.

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I have an F rev 511?

Color me interested. Message incoming. You prefer email or IM?

Elbows were off the table. I have manners. I can re shoot it if you'd like. I'll be goin back tomorrow anyhow.  Call it a mulligan?
Edit-Can we have a post of the perameters again?
And I can't see. I measured the wrong one.
Actual results, attempt 1?:
6.937-.224=6.713
6.713" group

Don’t have measurements, but my 551 on a LaRue riser seemed similar height to an EXPS3 (EXPS May have been a little
Lower). I’d just go for a new one of those and replace the hood if you so choose. You could always use an XPS if you want to use a riser.

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1/3 on a riser or bust

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