My first Clone Build: the MK18 CQBR

MK18 CQBR clone build
| March 22, 2021
Categories: Guns

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.

So why do people like to build clones? To many, it’s to build a piece of history. For our service members, they would like to build an 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, one being cost and the other being sourcing parts.

Clone Rifles is a great website to start with the identification and list of parts. That’s where I started. I wanted an Mk18 in particular for quite some time because it was proven, iconic, and still very practical to use as effectively today as it was when it was first implemented with our armed forces.

History of the Mk18, also known as the CQBR (Close Quarters Battle Receiver)

MK 18 build, side profile.

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

Based on my research, it was a SOCOM program to shorten the M4 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 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

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 CQBR Block II:

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 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 receiver, 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.


The Mk18 is definitely lighter than the M4A1 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!

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 anymore for you to worry about other than your threat.

California Compliance:

Yes, I absolutely hate having to put this on here but I do reside behind enemy lines and 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. 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.

The Brownell’s GRF trigger is a clean and fast trigger, 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!


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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