CMMG MK 17 Takes P320 Magazines?

yep, P320 magazines

If you carry a PCC or, uh pistol caliber “AR pistol”, for serious work, what is a defining criteria for it? I mean besides the obvious ones like reliability, ergonomics, portability? Well, how about what it feeds off of? I can’t think of a lot of sillier ideas than being required to carry the same 9mm ammunition in two different types of magazines. And fortunately, our friends over at CMMG feel the same way.

21 on tap and ready to feed from your P320 stash.

Almost every PCC on the market today either feeds from Glock magazines or comes in an option to feed from Glock magazines. And largely, that has been great. Glock mags are well supported by the factory, with up to 33 round options. And the aftermarket is rife with everything from drums to $13 range mags. In fact, one could argue that the strength of the Glock system is the magazine.

But are you going to let your primary weapon dictate your sidearm, in the year 2020? Well, CMMG is at least now giving you an option. The all-new MK17 variant of the CMMG Banshee 300 now runs on Sig P320 magazines. Which is hugely helpful. The P320 is the first handgun that made me seriously consider a swap from my normal duty gun, a G19. I have reviewed several options from the SIG line up, including the X5 and X-Carry, and you know if you read my reviews often how highly I thought of them.

Bazooka Green goodies from CMMG

Not to mention, the P320 is the future. As the winner of the US Army sidearm contract, with a subsequent pick up by the rest of the DOD, half a million P320 pistols are already allocated. Because of how Army acquisitions works, you can bank on that purchase fueling a huge accessory and aftermarket push over the life of the contract. If you made for instance, holsters. Would you build it for the new gun that might sell 5,000 guns this year? Or for the one with 500,000 guaranteed in circulation, before civilian sales even start? Me too.

Oversized mag release

So I am very happy to see this new Banshee hit the market. Now is it all sunshine and roses? Not exactly. As a factory option, at the moment, the biggest P320 magazine available is 21 rounds. The Mk 17 ships with two of them. And while 3rd party magazines do exist that are larger, we couldn’t test any due to availability. However, it is an absolutely safe bet big stick sized mags will both be available, and be prolific, in the future.

Tested with EOTECH 512

And how about that 21 factory SIG model? Well, we know it is durable. Not only did it ace the DOD tests, but I have been running mine for a long time now. Sticking in the MK17, it extends down to even with the pistol grip. Which means optimal bullets for the smallest possible overall height. A bonus for concealment, or use in vehicles. Less to snag really starts to matter in an environment of seat belts and headrests. And when you get right down to it, 21 is usually gonna be enough to get it done. For a frame of reference, I always run 20 round mags in my truck gun AR’s.

RipBrace 5 position brace

And then we have our Banshee. An absolute work of art in aluminum and steel. It has all the things we expect these days from a CMMG 300 series, which is to say a lot. It features a minimalist micro CQB RipBrace, to minimize snags. The Rip part means no buttons to press. Grap and pull, the brace snaps to full length effortlessly.

The trigger is a CMC single stage, a big step past mil-spec. Triggers are often overlooked in AR-type pistols, due to the fact we aren’t usually looking for sub MOA type grouping ability. But a good trigger is faster, as well as more capable of taking a difficult shot. We might not need this gun to print on paper at 400 yards. But the trigger still matters if you are trying to hit a moving bad guy in a sea of bystanders. Big points to CMMG for putting a good trigger in.

Excellent out of the box trigger.

Up top is an oversized charging handle, which is also ambi. The magazine release is all CMMG design and is absolutely huge. This is one of my favorite features of the Banshee series, an option I wish all my AR’s had. It alone is worth checking out at your local gun shop.

The barrel is only 4 inches long, which is not my favorite. But it is popular, so I understand why this length is the first offering. The bottom of the handguard does have a built-in hand stop, which is an excellent feature on a gun this size. CMMG was clearly thinking here, and I appreciate it.

Oversized charging handle.

The best part? The operating system, by far. Instead of a straight blowback design, we have a patented radial delayed blowback system. Basically, the CMMG Banshees take some of the energy of recoil and use it to unlock the bolt. The result is an incredibly soft shooting 9mm gun, with no compromise on reliability. Our test model ran everything we fed it, without the slightest hint of a hiccup.

Built in hand stop.

More you say? Good. Cause CMMG has it. From the factory, every Banshee 300 series comes with 10 cerakote colors as an option. No charge, it’s part of the package. Our test model is in Bazooka Green, which has really grown on me. I am loving the idea of throwing some color in my safe, after decades of black or FDE as the only choice. It really gives the gun a fun and unique look. I also highly recommend the color, midnight bronze.

Ambi sling attachment points.

Overall, this is an excellent development. Not only is CMMG arguably the best 9mm AR on the block, but now it has a different feed option. If you are moving to the P320 family of pistols, this is a highly recommended addition to the package.

MSRP $1549

For more information visit CMMG Inc website.

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About the author: Clay Martin is a former Marine and Green Beret, retiring out of 3rd Special Forces Group. He is a multi-decade and -service sniper, as well as 3-Gun competitor and Master ranked shooter in USPSA Production. In addition to writing about guns, he is the author of “Last Son of The War God,” a novel about shooting people that deserve it. You can also follow him on twitter, @offthe_res or his website,

{ 15 comments… add one }
  • Mark Taylor September 25, 2021, 2:54 pm

    I just purchased a CMMG Banshee MK17 and the trigger will not reset. Easily 50% of the time, after a shot the trigger will not fully reset, so I have to play with the safety to get the gun to fire. The ex-marine at the range I go to spent 30 minutes lubricating, tightening and adjusting the trigger to no avail. I sent an email to CMMG and they said it was “unusual” and yet the tech knew exactly what the issue was and offered to send me parts to replace. Now I find dozens of web sites with customers talking about the exact same thing. This is a known issue and yet they are still shipping $1600 guns that don’t work. And then expect customers to make the repairs they should have done in the first place. Buyer beware…if you are not a gun smith, you should not buy a CMMG Banshee.

  • Kane December 21, 2020, 5:16 pm

    I saved this article from a few weeks back as I was serious about getting a CMMG with a few more more inches of length on the barrel. One of my CCW’s is a Sig P-320 and I like the compatibility. One of the problems is that most firearm purchases are such a long shot and something like this is going to take a long time with serious money tied up with no guarantees. I decided for now to cancel plans to buy this firearm. Also, the BATFE seems to be intentionally establishing legal policies and later creating policy ambiguity.

  • Ogie December 21, 2020, 3:29 pm

    Is this legal in california?

    • area 52 December 21, 2020, 5:33 pm

      It’s consider a pistol therefore it has to comply with CA “handgun roster” . One requirement is if it’s semi auto it needs microstamping. So the answer is No it is not legal in CA.

  • jerry September 11, 2020, 12:17 pm

    Nice! Very nice. However, it does not appeal to me for a couple reasons. Why would I buy a pistol/carbine that uses $60 mags that are hard to get with all those perfectly good Glock mags are out there for $20? Still, I would sure wouldn’t turn one down if the price was right.

  • Rosser Farley September 8, 2020, 3:11 pm

    Great review from Clay with one minor correction, the Banshee 300 9mm upper has a 5″ barrel with a 4.5″ handguard. I just got one of these new Mk17 models, lower only, to go with the upper from my original Banshee 9mm Glock mag version – the Banshee 300 MkGs. I just don’t like Glock things and I currently have 3 P320s along with a s**tload of 17 and 21 round OEM P320 magazines, so obviously I needed this…! I also just ordered a pair of Promag 32 round P320 magazines for my Mk17 and I am hoping that they run okay.

    • isaiah November 16, 2020, 7:29 pm

      Any luck with those pro mag magazines?

  • ejeffreys September 8, 2020, 12:06 pm

    I am currently in the market for a “braced” 9mm AR platform (Glock mag model) but with a left side charger.

  • John Q. Public September 7, 2020, 12:49 pm

    Anyone else getting really sick of inflating the price of a firearm due to the magazines it accepts? This along with charging extra because “oh there’s no tax stamp!!!” with a shorter barrel and “it takes cheaper 9mm!!!,” I’m completely out at $1549 minus whatever few percentage points off of msrp. I was interested in this but there’s no way I would spend this much money on this firearm when parts to build an equivalent were readily available much cheaper just a few short months ago. It’s time we stop buying this crap for twice what it’s worth and show these manufacturers were not paying it.

    • Guido September 7, 2020, 6:03 pm

      Hello, Mr. Public

      I agree with your premise about gun prices, but your statement
      “…when parts to build an equivalent were readily available just a few short months ago.”
      rings true for the most part. However, if you attempt to source the parts today, as you alluded to, not only will they be prohibitively expensive, but also, unless you’re very cozy with a number of manufacturers, the parts are currently unavailable. Just waiting on endless backorder lists, and then paying somewhat inflated prices anyway.
      And the BCG system that Clay explains is not available separately anyway. Granted, it could be easily overlooked on a 9, but on a 10mm, for instance, it is an amazing improvement on felt recoil.
      While I agree there are multitudes of riders on only a few different bandwagons, I have to give CMMG prop’s for stepping outside the envelope and piloting their own wagon.
      To the innovative go the spoils!

      (BTW, the Banshee’s can be found for $200-$300 off MSRP, even in this feeding frenzy)

      • Guido September 7, 2020, 6:06 pm

        Almost forgot to mention, thanks for a great review, as always, Clay.

  • Ron Franklin September 7, 2020, 8:55 am

    Going to contact my dealer and check this out.

    • David C. September 7, 2020, 1:14 pm

      Better yet, buy directly from CMMG – the only caveat is the 10+ weeks wait due to workload – they build each one to order – not en masse –
      Trust me – it will be worth the wait – I have a Banshee 300 45ACP w/8″ barrel on order now for 6 weeks. Hope to hear from my FFL around the first week of October.

  • Robert Lopez September 7, 2020, 5:45 am

    Is this weapon available now and where can I purchase one immediately ?

    • Gary Metzger September 15, 2020, 2:27 pm

      Yes, is this available….MSRP ???

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