The CMMG Mk9 PDW is one of those guns often defined by what it is not. It is not a modern sporting rifle, exactly. It isn’t a 5.56. It is not a traditional AR pistol (if such a thing exists). But if you’re looking for something larger, faster, and more stable than a full-sized pistol, the Mk9 may be for you. If you are looking for something smaller and less powerful than an AR carbine, the Mk9 is an ideal choice. Not quite a carbine, more than a pistol: the Mk9 shines.
By the numbers
• Caliber: 9mm
• Barrel: 8.5″ medium weight profile
• Muzzle: A2 comp., threaded 1/2-36(9mm)
• Hand Guard: CMMG RKM7 KeyMod hand guard
• furniture: Magpul MOE pistol grip
• Receivers: Forged 7075-T6 AL M4 type upper, AR15 type lower
• Trigger: Single stage mil-spec style trigger
• Weight: 5.3 lbs (unloaded)
• Length: 25”
This Mk9 is a 9mm, but the pistol is available in 300 Blackout, and .22LR. Much of the specifications are easy to see in the photos. The one piece that deserves a bit of ink is the magazine. It is designed to hold 32 rounds, and the spring tension is seriously tight. It help to load on something solid as you’ll need to use a bit of bump-force to get some of the rounds seated, especially as the count rises.
The trigger on the Mk9 breaks at about 6 pounds. Just under. As it is described as a mil-spec style trigger, this seems appropriate. It has a touch of mil-spec style creep, too, but that doesn’t keep it from being functional. The break is sufficient for a pistol meant for close, fast, adrenaline-fueled use.
How do you hold the Mk9?
The CMMG Mk9 PDW is appropriately named. It is a great personal defense weapon. That it is a pistol seems almost like a formality. The CMMG Mk9 PDW is almost too big to be taken seriously as a pistol. I’m not talking about the legal definition; I’m referring to how it handles. You can hold it with one hand, like a pistol, but it isn’t balanced well for such a grip. You can cram two hands on the actual grip and hold it like you would a compact pistol, but that, too, leaves a lot of weight hanging out in front of the gun.
When you move your support hand up to the mag well or to the handguard, the balance problem goes away, but the pistol still requires some stability to perform reliably. If you hold like this while moving, finding the target is much more complicated than it would be with a light pistol or an actual carbine.
Adding a sling to the equation will stabilize the back end and help a bit, though I’d recommend using one with some elastic to give you a bit more flexibility. The Mk9 comes with a sling plate, which could be swapped out for a QD plate. The key-mod slots on the handguard can be used as QD slots if you want a two point, or you could just add a sling loop on handguard if you don’t want to monkey with the buffer tube. Key-mod seems to be the in-thing right now, as does QD. It would make sense to have a QD mount on the pistol from the factory, but it is easy to swap out.
Perhaps the easiest way to hold the pistol is with the buffer tube back in your shoulder. While it crunches you up on the compact gun, the stance is surprisingly functional thanks to the Mk9’s low recoil. There is no muzzle rise, and virtually no recoil, so nothing is going to bop you in the teeth. We put on an Aimpoint PRO, and mounted it a bit farther forward than we would on an AR with a longer length of pull, and it worked incredibly well.
If you want to take it to the next level of performance, slip on a Sig arm brace. The buffer tube on the CMMG is fluted on the far end and knurled closer to the receiver. The Sig brace slides on with a bit of effort, and is a bitch to pull back off, but once it is on there, the potential is really endless. And that is where the PDW distinction becomes much more relevant.
The CMMG Mk9 PDW is incredibly light. It isn’t a burden to carry, at all, so long as you’re engaging in really open carry. And it is small. The compact package, while big for a pistol, is more in line with typical short-barreled rifles. And it isn’t overpowered. Many who criticize SBRs say that you lose too much of the 5.56’s power when you cut down the barrel. With the Mk9, you are adding power to our typical expectations of the 9mm. A115 grain bullet will leave a Beretta 92 FS (which has a 4.85 inch barrel) above 1,100 FPS. The 8.5 inch barrel adds 1,000 FPS to that, maybe more. It is a modest increase, but still an increase.
Shooting the Mk9
I’ve covered the various handholds that make this gun a challenge. From here on out, you can assume I’m bracing the CMMG pretty well before I pull the trigger. If there were some law that mandated a pistol grip on the Mk9, my practical evaluation of the platform wouldn’t be positive. Yet I can hold the gun however I want, and the Mk9 comes alive when you give the back end some support.
We shot the Mk9 at distances ranging form 7 to 100 yards. The 9mm shoots relatively flat. When engaging a 12 inch plate at both distances, I was able to use the same zero from the Aimpoint. No hold over necessary. That makes this a really versatile pistol. Beyond 100, you may need to begin to compensate slightly.
Accuracy was better than you could expect from any full-sized 9mm pistol. At pistol distances, the gun shoots consistently. We had no problem connecting with 2 inch targets. And the light recoil means fast split times. Double taps are incredibly easy, and the point of impact only moves a couple of inches. A lighter trigger would make it even better.
We’re committed to reviewing guns honestly at GunsAmerica, and do our best to fairly document any issues we have with guns. When we first shot the CMMG, we had some strange jams. The rounds were coming off of the magazine and jamming into the top of the chamber. It happened once or twice a magazine and was a royal pain in the ass to clear, as the next round would be pining the errant round and the magazine into the gun. I was using Fort Mill 115 grain ball ammo for the initial review and that was what was jamming. The Fort Mill didn’t jam in any of the other 9mms I had. I could get other ammo to run reliably in the CMMG, but didn’t have enough of anything else on hand to test for reliability. The Fort Mill would jam into the chamber so hard that it would knock the bullet slightly to one side and bend the case.
I shoot a lot of guns, and I’ve never had this issue with anything. I called CMMG and they worked me through it. Their first thought was that it had something to do with the feed ramp. They sent out a new one and I made the switch.
I’m not convinced that the feed ramp was at fault. At the end of the review, I’m convinced it had something to do with this particular ammo in this particular gun. After isolating the Fort Mill, and swapping out the feed ramp, I was able to get the Mk9 to run magazine after magazine of everything. JHP, +P, steel case—the Mk9 didn’t care. And here’s the important part. When I called CMMG to ask about the problem, they immediately went into action. They were vigilant about following up with the fix, too. They provided excellent customer service and the pistol ended up functioning exactly as I’d thought it would. Can’t beat that.
All told, our experience with the CMMG couldn’t have been better unless we’d been able to magically anticipate the Fort Mill hang-ups. Once we had that cleared up, the Mk9 ran flawlessly. On a single point, with a nice pistol at your side (or a shotgun on the other side) the Mk9 becomes part of a great working combination. While it doubles up on much of the CQB work of a carbine, it does it in a more controlled manner than a typical 5.56. The 9mm may not offer the same terminal ballistics, but it isn’t as susceptible to over-penetration, either.
The more I get into these guns, the more I am convinced that the compact AR platform is the optimal choice for personal defense. In .300 AAC, and silenced, the platform would offer even more possibilities. Take some time and check out what CMMG is doing. You’ll like what you see. MSRP on the Mk9 is $1,099.95. Considering the cost of some of the more functional 9mm pistols on the market, that’s pretty good. And you won’t have to worry about holsters.