The MK18 CQBR: My First Clone Build

MK18 CQBR clone build
March 5, 2024  
Categories: Guns
Tags: CQB

This Mk18 Clone Build article first ran a couple of years ago. Some things have changed since then, but the amount of information contained herein hasn’t. Read on! 

Most recent update

Mk18 Background + Clone Build

Mk18 for Sale


Mk18 Build Update

I have a few updates for you regarding my “Mk18.”

1. I’ve taken off the Daniel Defense rubber Picatinny rail covers for looks as everyone can see and appreciate the RIS II Quad Rails. It makes the profile thinner, as the Mk18 RISII is already thicc. 
2. Next, I added the Picatinny Handbrake from Emissary Development. It helps with ergonomics and recoil management and can be used to push against a barricade.
3. A new product came to my attention that helps with signature reduction on weapon lights. One Hundred Concepts came out with the Light Cap and sent me a few to try. The reflector on your weapon light can give your position away since it is, well, a reflector. I covered my Cloud Defensive REIN Micro using the large size Light Cap. It’s held on with the included bungee cord and a thick rubber band. It stays on the front of the weapon light and flips up out of the way quickly when you need some white light. 

4. These updates have taken my clone even further away from a Mk18 factory SBR. However, functionality has improved with them attached. For the near future, I don’t see changing anything on it.

Flexing with those RIS II Quad Rails. They're thicc.

Flexing with those RIS II Quad Rails. They’re thicc.

Fifty Shades of FDE: Mk18 Build

I have been interested in building a clone rifle for many years. If you are unfamiliar with the term “clone build,” it means creating a copy of a very particular service weapon that is also period correct. It’s a niche community within the gun community and some are much more serious and committed to getting every single detail completely “clone correct.” I am definitely not a “truest” when it comes to clones. Keep that in mind as you parse through my Mk18 clone build. 

So why do people like to build clones? For too many, it’s to build a piece of history. For some service members, it’s a way to build a close or even exact copy of their service rifle since they don’t get to keep government-issued hardware once they finish their service.

A good portion of my reposts on @fiftyshadesoffde are of clone builds in varying degrees of clone correctness. Mondays aren’t complete without several #Mk18monday or #M4A1monday posts and you can’t forget about the #Mk12monday either. I hadn’t built one myself until the end of last year for many reasons: cost and sourcing parts. and are great websites to begin with; they can help with the identification and list of parts. If you don’t already know your preference – Mk 18 MOD 0, Mk 18 MOD 1, an earlier Close Quarter battle Receiver, etc. 

I began my Mk18 clone build with Clone Rifles. I wanted an Mk18 clone in particular for quite some time because it was proven, iconic, and practical. It’s as effective today as it was when it was first implemented with our armed forces. You could also of course, start with more than Daniel Defense Mk18 upper receiver (q.v.) from the very beginning, but there are pros and cons to both approaches (particularly if you want to go exact). Keep in mind that with recent changes in the pistol brace laws (implemented long after I wrote the original version of this story) you’re going to need to pay attention to NFA SBR rules. That would be a second tax stamp if you also put a suppressor on it. 

History of the Mk18, or CQBR (Close Quarters Battle Receiver)

MK18 clone build, side profile.

Side profile of my Daniel Defense based Mk18 Build. (Images by Muzzle Flash Media)

During my research, I learned this was a program initiated by United States Special Operations Command (USSOCOM) to shorten the M4 carbine platform to perform in tight CQB environments as well as continue to be effective out to 300 meters. This would eventually eliminate the need and role of the ubiquitous MP5 9mm submachine gun. The barrel was chopped down to a 10.3″ length to maintain the necessary velocity for the 5.56×45 round to still be lethal.

MK18 complete loadout

Complete Loadout with the Mk18 as the primary weapon; unfortunately, my Daniel Defense Mk18 pistol has become an NFA item.

The Mk18/CQBR platform was in service from the early 2000s in various iterations over the years and is still in service today with the latest Geissele MLOK rails. The purpose of this build for me was to have a reliable home defense platform and the parts selected represent that.

Mk18 for Sale

You can find your choice of Mk18 Mod x clone parts or a complete Daniel Defense Mk18 on sale online in several places. Here’s where we’d start. Be aware of any National Firearms Act issues (and any applicable laws in your area) associated with an Mk18 SBR. A true Mk18 is a short barreled rifle (in my case formerly a pistol with stabilizing brace). Don’t let that barrel length get you in a jam.

Where to Find Your MK18 For Sale

for sale

Mk18 CQBR Block II + My Parts List

The Mk18 CQBR Block II is the specific version that I was going for. When I was building it, I saw that Brownell’s carried the Daniel Defense MK18 Stripped SOCOM 7075 T6 aluminum Upper Receiver with Handguard Only. I told them that I was interested in building this clone and they helped make it happen by sending it right away. For a bolt carrier group, I chose the M16 Titanium Nitride Bolt Carrier Group (catalog 100-017-660MB) which isn’t clone correct but it looks nice and is TiN coated. The Knight’s Armament Company flip-up iron sights are absolutely clone-correct and what I went with.

The upper is the most identifiable and important of this build. The Daniel Defense Mk18 stripped upper makes it easy as it already has the correct black upper, Flat Dark Earth RIS II quad rail and barrel all together. The gas block isn’t pinned but put in with a set screw. I haven’t had a problem with it whatsoever, but it’s a good reminder to ensure your system is clean and squared away (and that you have a properly staked gas key). 

*If you don’t begin with a complete upper, you might check Ballistic Advantage for a suitable barrel. If other parts aren’t immediately available, it’s worth looking around for Colt LE6920 options. Some of those parts, like the buffer tube, pins, some springs, etc. are interchangeable. You can get pretty close to a Mk18 Mod with them aesthetically, too. 


The Mk18 is definitely lighter than the M4 carbine, but it’s still heavy considering today’s low-profile rails.

Muzzle Device:

I found a Surefire FA556 215A Flash Hider that was as close as I was going to get to the correct Surefire Four Prong SOCOM Flash Hider. The FA556 215A would be clone correct for the HK416. As long as it does its job at flash suppression and can take the Surefire Warden, I am good to go. As you can see, it gets very detailed and technical with these builds. At the same time, you have a lot of options since the Mk18 could take a lot from the SOPMOD kit.


Service members issued with the Mk18 had a lot of optics to choose from, Aimpoint, EoTech, Elcan, or Trijicon. I had an Aimpoint PRO with a Kinetic Development Group Sidelok mount that didn’t have a home so it easily snaps onto the flat top Mk18 receiver well. I chose the Aimpoint over the EoTech for its generous and long battery life. For a home defense gun, I don’t want to have to turn on my optic to get going, I’d much rather leave it on 24/7 and replace the battery every year. I spray painted my Aimpoint PRO in a medium and dark brown striped pattern to match the FDE RIS II rail.

MK18 beautiful blaster

The Mk18 is just a good-looking blaster! Oh, and beware: in the course of my research, I saw some entries that read 103 inch barrel. OBVIOUSLY, the Mk-18 has never used a barrel that was 8 1/2 feet long. An Abrams tank, maybe, but not a Mk-18. They mean to say 10.3″. 

Lower Receiver:

I grabbed the best quality lower receiver that was in stock at Rifle Supply, which happened to be a KE Arms AR15 lower. I registered it as a Pistol. This isn’t clone-correct at all but trying to source a specific Colt lower in today’s market isn’t something I cared enough about to go after.

Brownell’s sent me their AR-15 Lower Parts Kit w/ Geissele Rapid Fire Trigger (catalog 100-022-961MB), which I had my friends at Rifle Supply install for me. I am still not great at installing the lower parts kits, especially the take down pins. I didn’t have the patience to have springs flying all over their shop, so I watched it all installed in minutes.

The clone correct trigger would be the Geissele SSF or Super Select Fire, but since that is for a full auto NFA machine gun, the next closest option would be the SSA Trigger. I saw Brownell’s LPK that included their exclusive Geissele Rapid Fire Trigger in it, I thought it’d be a good option to try it out, and yes, it’s a very nice trigger with a clean break and short reset. The Reptilia CQG grip is one of my favorite grips and it went on the lower receiver.


Since I don’t reside in a state that allows for SBRs, I had to go with a brace. The SB Tactical SBA4 brace is one of my favorite arm braces available. It resembles a similar look to the clone correct M4A1 stock so that’s what I went with. For now, braces are safe to be a part of AR Pistols. Thanks to everyone who commented on the ATF site, the battle over braces is won for now but it’s far from over.

Weapon Light:

The clone-correct Insight WMX weapon lights have been discontinued for years making them rare and extremely expensive to source if you really want one. It might have been plenty powerful enough years ago, but it just doesn’t have the output that I want in a weapon light. At first, I went with the Cloud Defensive OWL, which worked great on top of the RIS II rail but the combined weight made it really front heavy. As soon as I got the Cloud Defensive REIN Micro in FDE, it took the OWLs place and for a little light, it has an impressive output of 1,300 Lumens and 55K Candela with a runtime of 35 minutes.

MK18 clone build with Cloud Defensive REIN Micro.

The REIN Micro saves on weight but not on output.

The REIN Micro is attached on the right 3 o’clock picatinny rail with a Haley Strategic Partners Thorntail from Impact Weapons Components and the remote switch is on the top rail sitting behind the KAC back up sight. This Mk18 isn’t going to be a safe queen or for showing off, it along with the majority of my firearms are tools and I need them to be practical and the most useful if I ever need to resort to them. Therefore, my weapon light needs to have as much output as possible so I can get the most information in low and no light conditions. The REIN Micro gets the job done while maintaining a small footprint.


A sling is an often-neglected piece of kit that is an important one. It acts as a holster for your rifle or in this case an AR Pistol, when you don’t need it up or at the low ready. Why is that important? If your primary goes dry or has a malfunction, it’d be better to drop it slung than on the ground. The RIS II rail doesn’t have a QD socket so I added the standard Magpul Picatinny QD mount. The SBA4 has QD sockets so I’m good there. I prefer two-point slings and have the SlyTactical non-padded sling for this build. The SlyTactical sling has a good-sized T handle that makes it easy for your support hand to find and glide the tension device to tighten or loosen it depending on your application. It does so very smoothly without any kinks.

Sling Retention:

I have grown fond of the NeoMag Sentry Strap and I have them on nearly all of my AR platforms. Having your sling held together and out of the way is helpful when storing it in your safe, in your bag or staged. To most it’s not a big deal until it is; you can get tangled up with your sling when you’re trying to deploy your rifle and end up costing you precious seconds to get into action. Sure, you can use a ranger band, but the Sentry Strap utilizes strong neodymium magnets to hold your sling and is easily deployed without much effort on your part and it’ll sort itself out without any more for you to worry about other than your threat.

Sidebar: Mk18 Mod1 + Eotech

Mk18 Mod1 notes by the Pew Pew Preacher

@pewpewpreacher dropping some knowledge using a Mk18 Mod 1 as an example. “Here’s a closer (and hopefully helpful) look at holographic sights since there are some who don’t know the difference compared to red dots…Since this EOTech has a holographic sight and not just a red dot that happens to have a similar reticle, the 68 MOA outer ring on the reticle is always 68 MOA regardless of how close or how far the optic is from your eye…When the optic is close to your eye, the reticle looks smaller inside the optic. When the optic is further from your eye, the reticle looks bigger inside the optic.                                                                                                                                                                                                                                                      However, you’ll see that the 68 MOA outer ring is the same diameter of the bullseye on the target regardless of the distance of the optic to the camera. That means you can use the reticle to estimate the distance of your target as shown in the picture. The picture is not meant to show the point of aim, but rather how to use the reticle to measure the distance of your target. Knowing the distance of your target will help you with your holdover so that you can properly aim for the distance of your target. This is even more advantageous when paired with a magnifier. The reticle is also helpful where you can use the bottom of the reticle to compensate for height over bore at CQB distances.


California Compliance:

Yes, I absolutely hate having to put this on here, but I do reside behind enemy lines. Like all Left Coast gun owners, have to be compliant with my AR Pistol I only am adding this on here because of the questions I will get from the pictures of my build about what mag release is on there. It is the AR Maglock with the Kingpin takedown pin. This is a decent way to have a maglock setup. Yes, I would rather not have it but it is what it is.

Edit: I am now in the process of sorting out whether to retire or SBR this.

Now onto how it works on the range!

Range Time:

With the ammunition situation the way it is currently and probably for the next few years to come, I did not shoot too many rounds through it. I took it to the local range to zero it in and then to an outdoor range to hit some steel. The Mk18 shot well and without any issues, not that I was expecting any. The Brownell’s exclusive Geissele Rapid Fire Trigger lives up to its name, I could send many rounds in quick succession as you can see in the still images. It’s too bad I just can’t afford to shoot much more with the GRF trigger as it is so much fun to press that trigger over and over again.

Fun to shoot! MK18 clone with Brownell's GRF trigger.

Brownell’s GRF trigger is clean and fast, and more importantly, priced very well.

This was my introduction into the world of clone builds and it is a good niche or sub-community to be a part of, albeit an extremely expensive one depending on how accurate you want it to be.

Full kit with the Mk18.

Full kit with the Mk18.

My advice is that if you’ve been wanting to build a clone, best if you get started sooner than later as things don’t stay in stock for long these days and will only get more expensive the longer you wait unlike buying a used car. There are some awesome clone builds out there, if you follow me on Instagram, you’ll see them, especially on Mondays as it’s always MK-xx Monday there – though not a Mk18 Mod every time! back Breach-Bang-Clear

Find what’s in stock, and where, and compare prices. 

⚠️ Some hyperlinks in this article may contain affiliate links. If you use them to make a purchase, we will receive a small commission at no additional cost to you. It’s just one way to Back the Bang. #backthebang 

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Fifty Shades of FDE

Fifty Shades of FDE

About the Author

Fifty Shades of FDE is a full-time LEO in California with about a decade's service in a very large metropolitan agency. He’s a husband, father and firearms enthusiast. He is a supporter of the Second Amendment and a proponent of law abiding citizens’ right to defend themselves with concealed carry permits. He runs his @fiftyshadesofFDE page on Instagram and writes gun/gear reviews on - when he's not writing for Breach-Bang-Clear, of course.

1 Comment

  1. Dennis

    For my “shorties”, I go with CMMG 22lr conversions. They run very well and allow me to do a lot more practice as 22lr is still available, even if it costs as much as 9mm did before the COVID insanitiy.

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