Gun Review: CMMG Mk3 LR-308 Rifle

Central Missouri Machine Guns, more commonly known as CMMG, started as a print shop in the early aughts before heading down the path to become one of the most well-known AR manufacturers in the industry.  Starting with barrels and uppers exclusively, CMMG now manufactures complete rifles under its own name, and has been doing so since 2005 – nearly ten years.  Each of their rifles is made in the USA and is protected by a lifetime warranty.

CMMG introduced and developed its .308 Mk3 line over the past few years, and now makes a half-dozen varieties of the Mk3 in varying configurations, ranging from $1,600 to $2,000 MSRP.  The subject of this review is the base model Mk3, with an MSRP of $1,599 (the upper by itself is MSRP’d at $999).  My research indicates that street price has hit as low as $1,100 on some variations of the Mk3 (complete rifle), however.



The Mk3 is an LR-308-pattern rifle.  This is emphasized because some readers may not appreciate that there are several varieties of .308 AR-style rifles, and accordingly, it may help to do some research on the matter before investing in a .308 AR.  User “TaylorWSO” at has a good post on the fundamental variations, although the information may be somewhat dated, being a post from 2008.  A Google search for “AR-10 versus LR-308” will fill in the informational gaps and likely provide you with enough material to make an informed decision.

Back to the rifle at hand, CMMG describes the Mk3 as “The perfect 308 WIN rifle for the tree stand or target range.”  The Mk3 employs an 18″ 416 stainless steel heavy taper barrel with a 1:10 twist, a CMMG RKM15 KeyMod handguard and an A1 length fixed butt stock.  The castle nut is not staked on the collapsible stock versions of the Mk3.  It comes with one Magpul 20 round .308 PMag.  The trigger is a standard, single stage GI-style, and the Mk3 lower is outfitted with a standard A2 pistol grip.


The 15-inch CMMG RKM15 free-floating handguard with KeyMod.

First, a word on KeyMod for those of you who are unfamiliar with this relatively new technology: KeyMod is a proposed replacement for the MIL-STD-1913 interface, sometimes referred to as “Picatinny rail.”  In other words, KeyMod – the product of a VLTOR/Noveske collaboration – was designed to replace the traditional Picatinny rail system that has been found on most AR systems since the late nineties.  KeyMod employs a keyhole-type system on the mounting surface (such as a rail) whereby accessories such as lights and lasers can be mounted without the use of tools if they have a KeyMod nut designed to fit in these “keyholes.”  The primary benefit is reduced weight through eliminating un-utilized Picatinny rail interface (which extrudes from the mounting surfaces), and a more ergonomic surface as it is ‘toothless,’ unlike Picatinny rail.  Dozens of manufacturers, including CMMG, have embraced this open-source technology, and it is taking the gun universe by storm at the moment.  You can find more information on KeyMod here.


Observe the reinforced takedown pinholes. This reinforcement is present on both takedown pinholes.

Fit and finish is very impressive after unboxing.  The test rifle had no visible flaws, and everything was tight and uniformly finished.  The stainless barrel on the Mk3 is a very attractive matte bead-blasted stainless similar to the Noveske offerings.  Compare this to other manufacturers such as BCM, who use polished stainless barrels.  The bolt release “ping pong paddle”, safety, and takedown pins all function crisply.


Note the striations on the backside of the ejector block and the lower ledge of the upper receiver.

The CMMG bolt is machined from 9310 steel, and the carrier from 8620.  The bolt is completed with a hardened extractor of S7 tool steel.  The carrier interior is chome-lined, and the carrier itself appears to be phosphated.  The key is staked.  While the staking is a little light (pictured), it appears to be acceptable.


Close-up of the gas key staking.



Note that the Mk3 has no sights, so you will have to purchase a set of front and rear sights for use with the Mk3.  Also note that the standard for BUIS is still Picatinny, so even though the Mk3 comes outfitted with a KeyMod interface, traditional Picatinny rail runs along the top of this gun, from the rear of the upper receiver to the front of the 15-inch CMMG RKM15 free-floating handguard.  Accordingly, this rifle still accepts your same optics from your standard A3-style AR.  However, where the RKM15 meets the receiver, there’s about an inch of flat surface without Picatinny teeth, as is common with non-monolithic handguards.


Close-up of the chamber and feedramp cuts.

The overall length of this rifle with the A1 stock is 38.5″, and the gun weighs 9.3 pounds unloaded.  To put this into context, a standard 16″ chrome-moly barreled Armalite AR-10 weighs 7.9 pounds, but for the extra accuracy and velocity provided by the 18″ 416 stainless barrel in the CMMG, the price you pay includes additional weight.  Moreover, the 17.1 ounce 6061-T6 extruded aluminum RKM15 handguard certainly contributes to that heft, but the free-floating RKM15 will also provide better accuracy and more mounting options over standard AR-style handguards.


But how do these specs come out in the wash?

General Observations:

Shooting this rifle, summarized in one sentence: If you’ve shot a high-end, stainless-barreled, GI-triggered AR-15 before, this is the same gun, but with more recoil.

In other words, there were not a lot of surprises in shooting the Mk3:  Unsurprisingly, the Mk3 was very accurate.  With Prvi Partizan PPU .308 FMJ 145grn, the CMMG punched four out of five rounds in one of my 100m strings into a .9″ hole.  To be fair, the first round was a flyer caused by my error, and even including that round, the whole bunch of five fit into 1.4 inches.  This is even more impressive considering this was fired from prone unsupported and with a zero-magnification EOTech optic.  Had this been fired from a vise or with a telescopic optic, I’m sure the Mk3 would have grouped even tighter.  A search of the typical forums have other users reporting that they obtain sub-MOA groups with match ammo, and groups similar to those I obtained (in the one to one and one half inch range at 100m) with standard ammo similar to what I used.


Four of five rounds of Prvi went into a .9″ hole at 100m.


Also unsurprisingly, there were no failures of any type, and no nuances or quirks with the rifle – everything worked as expected.  The standard GI-style trigger is what it is – the same single-stage trigger on every other stock AR.  Not to say it was good or bad, but it is definitely what you are used to if you have shot an AR before.

In all, function of the rifle functioned perfectly during the range session, and accuracy was excellent.


Negative Observations: 

And while the range session was impressive from a mechanical perspective, shooting the Mk3 from prone was physically taxing.  Recall that this rifle comes outfitted with an A1 stock and A2 grip.  While perfectly suitable for the lighter-recoiling 5.56mm AR15, these accessories don’t lend themselves to comfort with the more potent .308 variant.  If I were planning on purchasing an Mk3, these would be the first things I would replace, and represent my only (and therefore slight) reservations about this rifle.

First, as we all know, the A2 grip, though not a bad grip, is not very comfortable or ergonomic for most shooters.  For your average-to-larger shooters, the slim trigger reach can lead to too much trigger on the finger and a sharper recoil impulse than from an improved grip with a little more material in the tang, such as a Magpul M.O.E.  Fortunately, this is a cheap and simple replacement.

Similarly, the A1 stock can be brutal from prone.  At the risk of sounding fragile, when my range session concluded, I had a bruise where my right pectoral met my shoulder.  And I am no stranger to .308 rifles, but this was my first outing with an A1-equipped .308 AR.  (See the embedded video below and note that the recoil would gradually tilt my tightly-secured GoPro upwards after each successive shot.)

Range Session: CMMG Mk3 .308 AR from Pelican Handgun Instruction, LLC on Vimeo.

On a scale of FAL (more pleasant) to HK91 (brutal), I’d say that the experience with the A1 stock on this rifle was closer to shooting the HK91 with a collapsing stock (the HK91 collapsing stock is unceremoniously known as the “cheese grater” in HK circles).  But again, this is a cheap fix, and I think a rubber buttpad instead of the hard, plastic A1 trapdoor plate would do the trick – at least it seems to work for the FAL.  Most of you will probably drop a Magpul in place of the A1, anyways, so this may very well be moot.



In conclusion, the Mk3 is an excellent and well-made .308 rifle, apparently capable of sub-MOA accuracy with inexpensive factory brass-cased ammo.  And while my chief complaints relate to the recoil-management capabilities (or lack thereof) of the A2 grip and A1 stock, in the end, I would say it is better to have generic and easy to replace components such as the grip and stock to keep the price low, rather than to mark the cost up and sell a rifle to the user with a more expensive configuration that may not be suited to that particular buyer.  Basically, the buyer who drops $1,000-$2,000 on this rifle isn’t going to be daunted by an extra $100-$300 to customize those aspects of the rifle, so I would agree with CMMG’s approach in leaving the ultimate configuration up to the end user.  However, it might not be a bad idea to spend a couple of bucks to include a rubber pad for the buttstock for those shooters who have no plans to further invest in their Mk3.

Related to dollars and cents: As I said, my research indicates that this $2,000 MSRP rifle is anywhere from the $1,100 to $1,500, street price, and I quickly found a few on Gunbroker in the $1,200 range, NIB, however, I note that the Mk3s I have seen on the low end of the price spectrum appear to be older models without the KeyMod RKM15 handguard.  That said, if the quality of the older models of the Mk3 match the build and performance of the model I evaluated, I would say that $1,100-$1,250 for this rifle would be a steal.  In conclusion, if you are in the market for a .308 AR that has more amenities than your standard Armalite AR-10 or DPMS LR-308, you would be well-served to evaluate to the Mk3 for yourself.


James Reeves

• NRA-licensed concealed weapons instructor, 2012-present
Maxim Magazine’s MAXIMum Warrior, 2011
• “Co-Director” [air quotes] of TFBTV
• Former Regional Sales Rep, Interstate Arms Corp., MA
• Champion, Key West Cinco De Mayo Taco Eating Competition
• GLOCK® Certified Pistol Operator, 2017-2022
• Lawyer
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  • Unsooper

    I’ve been planning on building a DPMS LR-308 since it has a great reputation and I think it would be cheaper and more fun to build my own. Accuracy is extremely important though as I am a former competitive shooter. Would you rank them the same in that regard? $1200 is a very reasonable price for a .308.

    • James R.


      I can’t speak as to the LR-308 versus the CMMG specifically, however, if we are comparing CMV (most DPMS rifles) versus SS (the Mk3, for example), it’s accepted as fact that SS barrels turn out better accuracy and, strangely, a tick more velocity than their CMV counterparts. As someone who owns CMV and SS ARs, however, I’ve not been good enough to notice much of a difference in the accuracy department between the two barrels. It is likely, however, that someone limited only by mechanical constraints would benefit from the SS barrel over the CMV. I am sure Google has to have some with results from vised guns, which is what I would want to see before I made up my mind.

      One thing is for sure, though, you will get better accuracy form a free-floated handguard versus a traditional, non-floated handguard if you plan to support the rifle forward of the barrel nut.

      Good luck, sir, I hope this helps.

      • Unsooper

        Thank you all very much. That is just the sort of information I was hoping for. I am new to the AR platform having come from free floating bolt action rifles.

    • I spent almost $1000 more than that to build mine.. and it really isn’t that fancy. Everything about these is bigger, heavier, and way more expensive than an ar-15. $1200 seems like a steal to me.

    • CMMG does make a very good rifle. I’ve owned one since they started up. I’ve shot the 308 and agree with James they are accurate.
      I’ve had the privilege of watching them assemble rifles. One person builds the entire rifle from start to finish rather than have them go from station to station. At least it was that way about a year and a half ago and I doubt it has changed.
      When CMMG test fires a rifle they take it out back on the range rather than firing a short distance indoors.
      Pretty much it’s a family business that takes pride in their work. Another big plus for me was back when AR’s were hard to find at reasonable prices CMMG didn’t raise prices.
      A short ways down the road from Fayette and CMMG is Columbia, Mo. There’s a shop there that sells all the models CCMG makes. It’s called Black Rifle LLC. if that helps anyone.

  • Lance

    NAW James most pleasant .308 rifle to shoot is the M1A/M-14 I agree HKs suck in recoil. I say for the price get a M-1A instead though.

    • James R.

      Haha, thanks, Lance. I’d be lying if I said that I wasn’t hoping to troll a few M1A guys with that comment. I think the M1A/M14 is a great platform, I have always been a FAL guy, though. Thanks for noticing.

  • Nicks87

    9lbs. unloaded! Ach du lieber! It’s 2014 cant we make a .308 AR that doesnt weigh a ton? The price is about right though.

    • Blake

      “…for the extra accuracy and velocity provided by the 18″ 416 stainless barrel in the CMMG, the price you pay includes additional weight. Moreover, the 17.1 ounce 6061-T6 extruded aluminum RKM15 handguard certainly contributes to that heft…”

      Sure a lightweight .308 AR could be made; plenty of polymer and a sporter-profile 16″ bbl would do the trick. It would certainly be cheaper. It would also harm the accuracy & muzzle velocity and increase the muzzle flash & blast.

      Ask yourself: .308’s recoil is already pretty rough; do you think dropping two pounds off this rifle is a good idea? .308 is a long-range hard-hitting round. If you want a lightweight rifle, stick with .223.

      • Nicks87

        I dont care about the increased recoil. 308 is manageable even in a lightweight bolt action. What I want is something I can carry all day long while hunting but still have the magazine capacity, reliability and familiarity of the AR platform. 308 is a must (cheap, common, plentiful, more than adequate ballistic performance) and the price cant be out of reach for the average joe. It may sound like a tall order to some people but I believe the technology exists to make it happen.

        • Blake

          BTW speaking of polymer, Kel-Tec’s RFB weighs 8 lbs & takes metric FN-FAL mags &ltgrin&gt

          • Nicks87

            Lol yep, now if I could just find one for sale.

    • James R.


      Thanks for the comment. I generally agree with Blake’s reply – it could be lighter, but at the sacrifice of some performance advantages or cost.

      We will see, though, as I am set to review DPMS’ new lightweight .308 AR soon.

    • guest

      Genau. This (upper) is now certaily on my “must get” list. And… An a2 hider, which means hello monsieurs Brugger & Thomet!

    • android04
      • Nicks87

        I ended up getting a DPMS Recon 308. It’s super lightweight and shoots like a dream.

  • Well written James! I enjoyed it.

    • James R.

      Thanks, Phil!

  • JT

    I haven’t seen slots like that since Caldors went out of business

    • 101nomad

      I have not seen slots like that since LaGrange, Tx. ( seems I am late to this dog fight).

  • JT

    I haven’t seen slots like that since Caldors went out of business

  • David

    Just out of curiosity, an A1/2 stock does not use a castle nut, correct? I ask because you say the nut is not staked.

    Doesn’t the stock itself retain the locking plate, not a castle nut like on an adjustable stock?

    • David

      Correct, retain the takedown detente and spring.

    • James R.


      That’s correct. I’ll clarify in the article. The collapsible stock Mk3 models do not come with staked castle nuts. That did not apply to this particular model with the A1 stock. Thanks for picking that up.

  • cutamerc

    I know Mr. Reeves is an accomplished shooter, I would love to know what sort of groups he would see with a 10x optic. Thank you for the review.

    • James R.

      Thanks for the kind comment, cutamerc.

      Honestly, I am afraid to get anything past a 3x because I then place myself in a position where I will reveal how inferior I am to true distance shooters like F-Class competitors. I can get about as good a result as anyone could muster from anything under 4x when subject to the limitations of that mag level, but once I increase the magnification, expectations are going to go up, big time. I suppose the good news is that the nearest rifle range to me is over an hour away, and it is max 100m, so I guess my results would be satisfactory enough at what most truly accomplished and disciplined long rifle shooters would consider a chip shot.

      I will consider longer glass for future reviews.

      As a side note, while I used only an EOTech w/o mag in this review, I typically use the Weaver V3 fixed 3x with rifle reviews. I have not reviewed this scope (or any Weaver product) and I have zero ties whatsoever to Weaver, but I want to say I have a hard time imagining a better scope for ~$150.

      • cutamerc

        That makes perfect sense, especially since you were able to show great accuracy with an EOTech alone. Thank you for taking the time to reply, I look forward to future reviews!

  • James

    Thanks to James Reeves for a great review and also to on-point comments. This is what makes TFB is a great firearms blog.

    I’m a FAL guy too but I think I’m ready to move to a AR308 platform for 3Gun Heavy Metal. This certainly wets my whistle.

    • James R.

      Thanks, James. If you can really find one of these for $1100-$1200 like I’ve seen people claim on the forums, that obviously makes them a strong contender for 3G. If you get one, please follow up in the comments of this article – I’d love to hear about it.

  • 101nomad

    Looks clean. For around the house like my firearms simple. Good sights and a light. Can not afford a $2000 firearm tho. I do know a few people that can afford them and have a few. The prickly rails are meat shredders. The keymod is ok if you keep you fingers out of the keyholes. Seriously, I would love to have a .308 in that configuration. My max recoil tolerance is 12 gauge 2 3/4 00 buck, .308 rifle, .45 pistol. I think I could tame the beast. As is, I keep telling my .380 “you are a .45, not a .380……….”. My shotgun with adjustable stock and 18.5 barrel becomes the Arnold Shitslinger of the known world on a check and verify trip. One day I will do better. Having choices is wonderful.

  • James R.

    As a heads-up to the readership: It looks like PSA has a good deal on a 16″ Mk3 with a 2-stage trigger (I’d verify the trigger before I ordered, though) for $1350 today:

  • Yahoo

    before heading down the path to become one of the most well-known AR manufacturers in the industry – BS flag thrown! I think not!

  • 101nomad

    “Oh Lord, won’t you buy me a .308? All my friends have 5.56s and I need to make amends…………”……..This ain’t working is it?

  • red deer

    I just bought a cmmg lower 308, will most complete uppers fit this gun?

  • jim

    Just won one on GB penny auction. Looks like I have a heck of a deal at less than 900.00 nib. Hope so.