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If you’d told Nick a few short years ago that .300 BLK would have the market traction it does today, he’d have made a funny giggle, and started muttering, “The world belongs to the early adopters,” or some such nonsense. His earliest predictions seem to have come true and .300 BLK is here to stay. And the kings of the .300 BLK world seem to be the pistols built around Eugene Stoner’s beloved AR system. As it goes, a great many manufacturers have jumped in with both feet, bringing .300 BLK AR pistols to the market. CMMG’s offering is the MK4 PDW . . .

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To this point, I have avoided owning a .300 BLK gun of any type. The ammo costs and availability have always given me heartburn, but a quick check of GunBot shows a plethora of sub $0.65/rd offerings. It still isn’t down in the realm of where .223/5.56 has settled, but it is approaching a number where plinking is definitely possible. The other major factor that has kept me away is the acquisition cost of one of these guns. Sure I could build one (and I just might!), but factory offerings still seem to be several hundred dollars higher than their .223 counterparts.

Last, to really realize the true benefit of .300 BLK, you need a short barreled rifle, and a silencer. I have not yet forked over the money for either item, but I did recently form a trust, so the reality of a .30 cal can and a piece of paper that lets me have a shorter barrel can’t be that far off. For all those reasons, the CMMG has stirred a certain bit of excitement within my soul, primarily because of its price. The gun I’m reviewing retails at $999.95, but Bud’s Guns lists it at $794. That’s a very reasonable price for any factory AR, and if this thing runs reliably and shoots well, makes it one hell of a value.

Tack on ~$75 for an actual stock, pay $200 to the Fed and for a touch over a grand, you’ve got a legit SBR. That’s a very, very compelling reason to give the CMMG a very hard look. If you’ll remember, the similarly sized and chambered MK109 that I reviewed from PWS had an MSRP number just shy of $2000 but was finicky about ammo and served up group sizes in the 2 MOA range. If the CMMG gun can manage that for less than a grand, it stands to be a very interesting pistol.

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Full disclosure here. I haven’t yet shot this gun. I have however, dry fired it about a hundred times and held it out at arms length like a pistol. I have not shouldered it for fear of a black clad ATF agent knocking down my door and shooting my dog. I imagine that it shoulders pretty well, but I just can’t risk the dog like that. From a cursory overview standpoint, there are a couple of things that stand out.

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First and most pressing, the trigger sucks. Badly. As most milspec triggers do, this one breaks at a bit over seven pounds, and has enormous amounts of stacking and creep along the way. I’ll fire it for accuracy with that trigger, but methinks a Timney that’s sitting in the parts pile might take its place fairly quickly lest I come down with a crushing case of carpal tunnel, ending my brief writing career. But hey, the gun costs less than a grand, the trigger had to suck.

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Also worth noting is how rough the whole gun feels both to the touch and in operation of the controls. Flick the safety or cycle the bolt on a Noveske or LaRue gun and you’ll think that the engineers from Mercedes got into the gun game. Do the same on this gun, and you’ll feel the grit and creaks way down deep in your soul. The buffer spring made so much noise that I finally gave up, pulled it out, and rubbed it down with Sil-Glyde. It came out of the box totally dry, and I’ll degrease it just as soon as I get to shooting it to see if it runs dry, but for dry fire practice, I needed to keep the peace.


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Otherwise, it seems to be a fairly bone stock AR pistol build. All the parts that are supposed to be there are, and despite some roughness in overall finish, it appears that this is a working class gun. The marketing guy who handles the CMMG relationship warned me that the short barrel .300 BLK guns don’t like to cycle subsonics without a can, something that I’ve experienced first hand. Otherwise, he told me to go shoot the hell out of it and write an honest review. I plan to do both.

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47 Responses to Just Arrived: CMMG MK4 PDW in 300 BLK

  1. I still do not comprehend the draw or the utility of AR pistols. No matter what Sen. De Leon might think, they are really not concealable, they are heavy, awkward and inaccurate, and particularly in .223, underpowered. What’s the point?

    • They are much easier to enter and exit a vehicle with, than a normal sized AR. They are also much easier to handle in CQB.
      If SBR were legally allowed without all the hassle, we wouldn’t have AR pistols, but reality is reality.

      • I don’t think the California police would approve of me carrying a loaded unconcealed “pistol ” like this inside my vehicle (except unloaded and in a locked case), nor do I think that I will EVER be involved in “CQB” where a handgun won’t be up to the task at hand , especially in view of our 10 round mag limit. I’m just not an operational operator, I guess. Nor is Tyler’s route to an SBR available here–no SBRs, no silencers, no machine guns, no .50 BMGs allowed (other than those grandfathered in). Despite the popularity of these “pistols” in California, especially for 80% builds, I will pass.

        • I don’t think the California police would approve of me carrying a loaded unconcealed “pistol ” like this inside my vehicle (except unloaded and in a locked case),
          —————-
          As long as you follow California law, the States personal approval doesn’t matter. Be honest, the State of California doesn’t approve of you having even a handgun.
          ================
          nor do I think that I will EVER be involved in “CQB” where a handgun won’t be up to the task at hand , especially in view of our 10 round mag limit.
          ————————-
          I hope you are not involved in any combat, much less CQB, but just as I hope you don’t have to use a fire extinguisher, being prepared means including scenarios you would rather not happen.
          ================
          I’m just not an operational operator, I guess. Nor is Tyler’s route to an SBR available here–no SBRs, no silencers, no machine guns, no .50 BMGs allowed (other than those grandfathered in). Despite the popularity of these “pistols” in California, especially for 80% builds, I will pass.
          ————————-
          The advantage of a 300 BLK AR pistol is that if things really go south, for instance a major earthquake that disrupts food and water delivery, you can swap that 300 BLK upper with a standard 16″ upper, depending on what you think you may encounter.
          As you said, you can’t get a SBR in California, so if you want the ease of use of a shorter rifle, you have to make do with an AR pistol.

        • Xantro:
          1. Without a CCW, you can only carry a firearm in a vehicle in accord with FOPA, as I have described. California only allows open carry out in the woods. And somehow, I do not think ANY sheriff or COP will approve an AR pistol as a concealed carry firearm. It is simply not a concealable weapon, even if it is technically a pistol. Which means unloaded and in a locked container, period.
          2. I have no battle training much less experience, and I ain’t no spring chicken, so not only am I not planning for any CBQ, I am not going to train for it either. Plus I do not live near any major fault line, tornadoes are extremely rare, hurricanes never, and the nearest volcano is 60 miles away. The worst risk is smoke from a forest fire up mountain, since i don’t live in a grassland fire zone either. We have no gang filled ghettos, no targets of military or terrorist value. So I could care less about CBQ. Which leaves me with an inaccurate plinker. For a handy gun, I’d rather have an M1Carbine that is short, light, and good past 100 yards. (I only wish it had better bullet selections.)
          3. If I already have a long barreled upper, what do I need one of these?

        • So the platform doesn’t work for you. But because it doesn’t work for you, you can’t comprehend how it doesn’t work for others? Definitely a Californian.

    • Its still a rifle round vs a pistol round at the end of the day. A very inconspicuous bag i.e.guitar case and its a wonderful truck gun. IF we didnt have that dang ol NFA shenanigans, we could all just SBR everything all willy nilly like free men.

    • You could greatly expand your hunting season, depending on your state’s regulations, while retaining most of the advantages of a rifle.

    • AR pistols with their stupid looking buffer tubes are so damn ugly.

      If you absolutely have to have this type of pistol at least put the Sig brace on it, or better yet just get a Draco type AK pistol instead.

      The AK pistols look cooler, run more reliably, and lose less velocity with the short barrel (7.62×39 vs. 5.56).

      • .300 BLK has really fired up the AR pistol market, since even supersonic .300 BLK reaches near maximum velocity in 8-10 inches of barrel, and the subsonic is tuned for the same.

        I won’t argue short barrel .223 vs 7.62×39, because there’s no argument. Short barrel .223 is kind of sad.

        I think I’d try to build one with a Troy PDW-type stock kit, like Safety Harbor’s KES because Honeybadger.

    • They are quite accurate. I could take a newbie to the range and they’d be hitting the x ring at 50 yards all day over a traditional pistol. You could easy punch out past 100 yards with a 300/223 with 7 inch barrel if need be. Sounds like you could use some time behind one someday.

    • The point is that the government is hung up about rifles and shotguns with short barrels, and pistols with shoulder stocks, because of an law from 80 years ago that is inexplicably still on the books and was at the time a de-facto ban on what they perceived to be the weapons of choice of gangsters and rum-runners.

      The current generation of work-arounds are an ugly but effective response, and also an option for those who object to paying a $200 tax to the ATF for the permission to exercise a right the way they see fit.

  2. “I have not shouldered it for fear of a black clad ATF agent knocking down my door and shooting my dog.”

    Really? Anyone else see this? What happened to this country?

    Government needs to be pushed back.

    • That’s why I’m donating to the campaigns of Rand Paul, Scott Walker, Ted Cruz, Jeb Bush, and Chris Christie.

      (Just kidding on the last two.)

      • You might as well donate to Hillary and Barack, as Bush and Christie. They are all big gov statists.

        The frst three guys you mentioned are a bit better.

  3. [T]o really realize the true benefit of .300 BLK, you need a short barreled rifle, and a silencer.

    Which explains why there’s so little of such ammo sold in MA, and why none is needed.

  4. “Last, to really realize the true benefit of .300 BLK, you need a short barreled rifle, and a silencer.”

    Pretty much the sole reason I havent built one yet. Im definitely interested after reading articles and so many comments about the round. One day Ill have an 8 inch SBR with a can on it, one day…

  5. > .300 BLK guns don’t like to cycle subsonics without a can, something that I’ve experienced first hand.

    Bollocks. A properly-built gun (using a pistol-length gas system) cycles .300BLK just fine without a can. I’ve built maybe 6 ARs and my first .300BLK build – 10.5″ barrel – runs perfectly with super- and sub-sonic ammo unsuppressed.

    Please tell us what gun you shot that wouldn’t cycle unsuppressed so your readership knows to avoid ever buying anything from them. They would have to be either criminally incompetent or actively trying to screw their customers.

    • The only time I’ve seen cycling issues with .300BLK and no can is actually with the longer barrels. .300BLK really doesn’t like those 16″ carbine gas barrels you people are using while waiting for your SBR paperwork. You’re doing it wrong and should have started with a pistol.

  6. 300blk is too mainstream for my taste now. Very few look at you and think “What an idiot” anymore.

      • Sorry, I communicate poorly, I was being facetious. I do prefer odder weapons though and mostly keep my preferences to myself (with the exception of this blog sometimes).

    • “300blk is too mainstream for my taste now. Very few look at you and think “What an idiot” anymore”. LOL, so you think it is a good thing if others look at you and think you are an idiot ? Is that your goal ? 😉 I can understand wanting to stand out from the crowd but I don’t quite get aspiring to look like an idiot.

      • Well, not exactly an idiot, but maybe a weirdo or perhaps something like a poorly dressed, un-groomed and ill mannered fop;-)

    • Which is why I like the concept of the .277 Wolverine more that 300 Blackout. I’m not interested is a SBR or a silencer, due to cost and paperwork, but I want a heavier bullet that the 5.56 offerings.

  7. Logically very true. Shooting 300 BLK means you’re using a silencer and/or an SBR. If you have neither, then you missed the entire point of the caliber.

    • I love my carbine and SBR 300’s. Gives you a lot more options. Just because it excels at two things really well doesn’t mean its a 2 trick pony.

  8. I just never got the AR and AK pistol crap. Converting it to an SBR with the associated jumping through government hoops might have some merit, but I think the 7.62 X 39 mm round might at least be cheaper and more available than .300 BLK.

    • AR / AK pistols by themselves are pretty much novelties, but they do (well, they might) provide that upgrade path to SBRs.

      The AR platform offers more flexibility in the long run if you go the pistol -> SBR route. A registered SBR lower can take all manners of uppers in a variety of calibers with less worry about barrel lengths. And if your SBR starts its life as a pistol you could even convert it back to a pistol. If you’re willing to jump through all the hoops and play the long game then the point of an AR pistol could be a legal pathway to owning a rifle lower that you can customize and reconfigure with fewer worries about silly accidental felonies.

      • Wait, now, I thought that you could not switch back and forth between pistol and SBR under NFA. Are you saying you can register a pistol as an SBR and then convert the lower and be about your business, then later switch back? But not the other way, converting an SBR to a pistol? I know the whole mess is insanely stupid, but that is also unbelievable.

        • The SBR tax effectively allows you to put a stock and vertical foregrip on your pistol. You can already put stocks and foregrips on rifles, or leave either or both off, as you like.

          Essentially, SBRing your pistol lets you put a stock on your pistol lower, if you want to. you could already combine your pistol lower with any upper you like, so long as it didn’t have a vertical foregrip. (now it can!)

  9. I don’t get it. I’m not against it, I just don’t see the big deal. I only ever hear of this round in here. I’ve never seen it for sale anywhere at retail. I’ve never, to my knowledge, ever seen a rifle in this caliber at any range. I don’t see any advantages to it, but a whole lot of SBR and silencer hassles and expenses.

    Seems like just the latest flavor of the month for the tacti-toys crowd. Not that there’s anything wrong with it.

    • 300BLK really does make the most sense with SBRs and silencers. Since all the powder burns in a short barrel an SBR is the way to go. Silencers make the most of heavier, subsonic loads.

      The real advantage of 300BLK, if you do bother with the hassle and expenses, is a great deal of ballistic flexibility with a single lower. So invest in a nice SBR lower with a great trigger and a couple uppers and you can shoot supersonic 300BLK with AK-like ballistics, subsonic 300BLK with .45ACP-like ballistics or 5.56 for typical AR ballistics. All with the exact same trigger and stock.

      For what it’s worth I saw 300BLK supersonic HP (Remington) at WalMart the other day, so it has arrived. Ammo prices have dropped a lot in the past year or so that I’ve been watching.

      • > For what it’s worth I saw 300BLK supersonic HP (Remington) at WalMart the other day

        That…is friggin’ awesome.

        I really regret all the .223 brass I left on the range in the past.

      • 300BLK is magic for reloaders. Powder use for supersonic is basically identical to 357 magnum loads (19gr H110), Sierra makes a super cheap .30 110gr hollow point for plinking (not to mention surplus 147gr pulls), and brass is everywhere.

    • If you’re not playing in the NFA world, you’re right, this caliber isn’t a big deal to most shooters. But it’s definitely not just some flavor of the month or a passing fad. Every major (and minor) brand in the firearms industry is already doing something 300 BLK related.

    • “I’ve never, to my knowledge, ever seen a rifle in this caliber at any range”

      How do you think you would have recognized one if you saw it? Every part other than the inside diameter of the barrel are exactly the same as a 5.56. It looks like an AR, because it is an AR. Lots are SBRs, but just because its an SBR does not mean it’s .300 Blk. Just because it has a 16″ barrel does not mean it ISN’T .300 Blk.

  10. Bravo Company Manufacturing (BCM) announced support for the 300 Blackout in the future on their Facebook page. “It’s coming. Not today. Not tomorrow. But soon. BCM 300 Blackout.”

  11. Will be really interested to see your results on the range. I LOVE 300 BLK, but seems to be a bit of a b*tch to get a reliable shortie platform that cycles it well, or maybe that’s just been my experience. It’s either an under-gassed piston (like the Mk 109), or an under or over-gassed DI, etc. Honestly, I don’t even care as much about shooting subs un-suppressed. 110 gr Barnes Tac TX supers out of a free floated 9″ barrel is about as much ballistic joy as there is in this world – Soft-shooting and hits like a ton of bricks. I’ve had some issues with my AAC MPW 9″ that are still in the process of being resolved. Maybe that is affecting my judgement. I’ve also heard of course of the issues with the spring in the auto-regulating gas systems on the new MCX which will remain un-spoken of further. Once you find a RELIABLE 300 blk shortie AR platform, please let me know so I can purchase it. I’m still in my experimental phase and it hasn’t been cheap or quick to get through it. And now that i have the taste of the sheer joy of a 300 Blk super out of a FF 9″ barrel, I am anxious to make this my platform of choice… once I can find something as reliably-cycling as a 5.56 middie AR

  12. “300 BLK is here to stay” I keep hearing this and we heard it about 6.8 SPC but yet I don’t see rifles chambered for these calibers at gun shops nor do I know people who own them. IMO its just another fad for the suppressor crowd and people that have more money than sense.

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