CMMG MK9 PDW

Disclaimer,  I am not affiliated nor employed with any of the companies mentioned in this review. I have not been compensated from any company and the opinions below are only based on my personal experience with the products and or companies.

Background, I have been on the fence about buying a 9mm AR platform for a while now. I have shot a few and loved how they shot and how much fun they were. I searched local shops as well as all over the net and found many parts for the 9mm platform but not a lot of complete platforms in my price range. The first thing I noticed was how much more the 9mm platform and the parts are compared to a 5.56. I assume this is due to limited companies producing these parts and supply and demand. I also noticed that the 9mm parts don’t always play nice together like they do with a 5.56 build. So my search continued for a complete 9mm platform. This way, if there was an issue, it could be handled by one company, and not 4 different companies pointing fingers.  Sure, I could have just bought the SIG MPX but that’s not exactly what I wanted and really didn’t want to pay that much either. I deal with a few online suppliers on occasion, one of which being Primary Arms.  They had the MK9 PDW on sale for $850, which was a great price, so I called and confirmed it was in stock and ordered it right away. Marshall and his team shipped it out very quickly and my FFL had it in about a week. It was shipped in its original box and then boxed again.

Unboxing, The contents in the box included, (1) MK9 PDW, (1) Cable Lock, (1) 1 sample of Slip 2000, (1) ASC 32 Round (Colt style SMG ) Magazine, and a Manual for an ar15 (Not the MK9). It was well packaged and sealed in a plastic bag. When I took it out of the bag, I noticed a very small blem on the lower. There wasn’t any damage to the bag or the boxes so it must have come from the factory like that. While this wasn’t a deal breaker, it was slightly upsetting for new purchase.  Since I bought it for over $250.00 less than retail, I decided to keep it and get over it. The upper and lower are forged aluminum and not Billet like some other companies but this didn’t matter to me. The upper appears to be a standard ar15 upper with a 9mm deflector and half port cover. The MK9 PDW upper comes nicely equipped with 8.5” barrel with a standard bird cage flash hider, and a slim 6 hole Keymod rail, (but no detachable rail sections). The Keymod fits very tight to the receiver using a proprietary barrel nut making it appear almost seamless to the upper. The rail also has a QD sing port on both sides, just behind the last key hole. The upper does have a gas hole and a forward assist, but neither is used. The lower is a dedicated 9mm lower with a beveled magwell, standard milspec trigger and safety, sling loop (Not QD), Magpul MOE Grip, Magpul trigger guard, 9mm buffer, carbine spring and knurled pistol length buffer tube. The 2 halves matched up perfect with very little play between them.  To help keep the costs down, CMMG does not include sights on the MK9 PDW or MK9 T, which are usually a personal choice anyway. My only addition to this nicely equipped firearm was a Blade brace for added comfort when cheek welding. The tube is slightly small so the Blade wasn’t a perfect fit, but nothing a little tape on the tube couldn’t fix. In fact it now fits nice and snug. I also added a set of Magpul MBUS sights and a Bushnell TRS-25 (for now).   The initial cleaning removed a good bit of carbon from the barrel and bolt, but it didn’t take too long and the MK9 and the mag were nice and clean, and ready for the test.

At the Range, I took 4 (Clean) ASC 32 round mags loaded with 115 Blazer Brass, 124 Blazer Brass and some 115 Remington UMC to the range. I locked the bolt back inserted the first mag and let the bolt go. Squeezed the trigger and it shot great. POA vs POI was very good. Pulled the trigger again and, nothing happened, so I inspected the chamber to find a stove pipe. I tried all 4 mags and different ammo and the same thing happened. It would shoot 1-2 rounds with week ejection and the 2nd or 3rd would stovepipe.  From what I read and researched it was the ejector causing the issue (CMMG confirmed this). The ejector needs to ride high and tight to the bolt channel in order to eject correctly.  After a couple small tweaks it was up and running like it should, and ejecting very strong. I shot another 250 rounds alternating between all 4 mags and all 3 ammo choices without a single malfunction, whether I was shooting fast or slow. While only shooting steal targets out to 20 -25 yards, the accuracy was spot on and consistent.  The initial performance was discouraging, but I am happy it was a simple fix and hope it continues to shoot the way it should. If not, CMMG does have a Lifetime warranty on their products that I can use if need be. I have heard nothing but good things about their service, so I have no doubt it would be taken care of.   The ASC mags worked great with the MK9 too. All 4 mags held the bolt open after the last round like designed and all 4 mags took the full 32 rounds without any issues and fed the MK9 without any problems. The TRS-25 held zero and was not affected by the recoil what so ever.

Cleaning, Since the MK9 is a Blow Back system; it tends to get pretty dirty.  I have shot thousands of rounds of Blazer Brass from other firearms and have never seen a firearm this dirty. I am not 100% sure the Remington UMC was not a fault either. This was the first time I used the UMC and it very well could have been the main cause.  The MK9 breaks down just like a normal AR, with 2 pins, but be careful when separating the lower and upper as the bolt never locks into the chamber like a normal ar. When separating the 2 halves the bolt likes to slide back but won’t come out, due to the charging handle being latched.  The bolt/BCG is slightly different however. The bolt is actually the BCG and the only parts to break down are the firing pin and spring, as well as the extractor and spring.  I took the firing pin and spring out of the bolt and noticed very little carbon, and the pin was not damaged and showed no signs of wear. The lower had some debris that needed swabbed out but wasn’t that bad. The upper and the barrel was where the mess was. The barrel took the most work but came out spotless with a little effort.

Conclusion, If you are looking for a fun AR based 9mm platform keep CMMG in mind. You will be hard pressed to find a quality complete platform at a better price. If you look around long enough, you can find them for $100-$250 off retail. Primary Arms would be my first place to look since the customer service is top notch and they have never let me down.  I chose the MK9 PDW for personal reasons, but I wouldn’t hesitate buying any of their products.  If I found the MK9T carbine around same price I would buy that in a heartbeat.   For the most part, the fit and finish as well as detail to construction are very good. While there was a small issue at first, it was an easy fix and I know CMMG stands behind their products. The MK9 has very little recoil and is nice and smooth to shoot. It comes nicely equipped and the accuracy is great with the 8.5” barrel length. The ASC mags feed the MK9 without any issues and are quite a bit less expensive than the comparable Metalform mags.  Overall I am very pleased with this purchase and have no regrets. If I had to be picky, it would be nice of CMMG to include at least one rail section for their Keymod rail and maybe some swag to advertise their great products.  The only real negative is I will need to buy more ammo to feed my new favorite toy.



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Update
Yesterday I shot the Mk9 in a steel fun shoot at my local range. I was using Blazer Brass 124 grain the entire day. I am happy to say, it performed awesome. Not 1 single issue. The range was out to about 20 yards maybe a little more or less on some stages. It made quick work of the plate racks, 4x4 plates, poppers and especially the Texas star. I am so happy and have no regrets about buying this fantastic firearm. Before, I was using the 15-22 for steel fun shoots which did great too. However, using a .22 on steel isnt always effective and sometimes requires 2-3 shots to knock down the steel. Since the The MK9 is so accurate and. A 9mm, I had no issues knocking the steel down In one shot. This may save me a few cents in the long run, plus it's a blast to shoot.   I have found my new steel gun.

Good write-up.
Here's mine:


Mine has been absolutely flawless since I've owned it. Your experiences are slightly difference than mine. Mine hasn't been excessively dirty - in fact my 556 AR gets far more dirty (I shoot both 100% suppressed).

Mods I've done to mine:
MAS 7oz extended buffer
Sprinco Red spring
Shockwave brace
Ruger BUIS
Bushnell TRS25 (not pictured)
Kaw Valley 4.5" barrel (not pictured)
Removed about 1.5" from the keymod handguard (not pictured) so an extended flash can could be mounted/unmounted
Slim Flash can - tucks under the handguard nicely, only about 3/4" sticks out. Makes it so I can shoot unsuppressed, but still have about 2" of the can tuck under the handguard.

That looks great. Did you change the buffer and spring due to the can? Did you put anything on the buffer tube to take up the space between the brace? If you get chance, try and take a good picture of the ejector and how it rides in the bolt channel. I would like to compare it to mine. I just got off the phone with CMMG and they said occasionally the ejectors need tweaked, but they Usualy stay that way once they are adjusted. He did mention if I ever have a issue to give them a call and they would send out new parts or take it back and adjust everything as needed.

No... kinda.
The extended buffer should prevent the bolt catch from breaking (supposedly this happens if the bolt is allowed to travel too far forward before hitting the catch). The heavier weight buffer is supposed to keep the bolt closed a fraction of a second longer after firing, which in theory will reduce port noise and reduce the impact of the buffer hitting its reward stop. In effect, it was hard to notice any difference. Maybe recoil is a bit smoother.

Not sure what you mean?? Brace slid right on the tube, tightened with the set screw.


Will try that. CMMG definitely gets a thumbs-up from me. Quality 9mm package that just works. I also use ASC mags without any issues (can't beat $14ea).

Where are you finding the ASC Mags for $14?

The very first hit on google....

My 9mm AR is the most fun gun I own and gets shot the most. I would not worry about how dirty it gets. It is just the nature of a blow back. I've ran mine over 1000 rds without cleaning and it had no issues with reliability. The lower does get dirty, but I just hit it with an air compressor every once in awhile. The gun will stay a little cleaner if you switch to a 7-8 oz buffer.

See original post for an update.... This thing is simply awesome.