Earlier this week we posted CMMG’s press release announcing their new MkG45 Guard, a .45 ACP carbine with a “radial delayed blowback” action. A visit to the CMMG booth at the NRA Annual Meetings netted some hands-on time and more details about the gun’s unique action and last round bolt hold-open design . . .

Externally, it’s a modern pistol caliber AR carbine with a billet lower designed to accept GLOCK magazines — via a well-flared magazine well — at the proper angle. The ejection port is enlarged to clear those chubby .45 ACP cases, and the magazine release is oversized as well. Otherwise, it’s AR-15 dimensions and accepts standard AR triggers, grips, charging handles, forward assists, stocks, dust covers, etc.

Over to the BCG, it’s actually very much as we speculated in the comments on the press release post. The bolt lugs are angled at the rear, allowing the force of the case to spin the bolt, unlocking it from the barrel extension after the rotation-caused delay.

The “gas key” is unique as well. It isn’t actually used during the firing process, of course, but is still needed to have a functional charging handle. The design of the MkG45 gas key prohibits the BCG from being inserted into a standard AR-15 upper, which is a good thing because firing a .223/5.56 on a blowback system — radial delayed or not — wouldn’t be pleasant.

Most pistol-magazine AR lowers simply forgo a last round bolt hold-open. Those that have this functionality aren’t exactly lauded for reliability, with many running a flimsy, flex-prone bar all the way from the AR’s bolt catch location to the front of the magazine. On the MkG45, they’ve necessarily used a bar that extends to the front of the magazine, but it’s firmly affixed to the receiver at front and rear and rotates on pins. Rotating to the side, rather than lifting up in the front, provides a more secure, reliable, stiffer interface.

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20 Responses to Hands-On With CMMG’s New MkG45 Guard

  1. I personally think it’s a cool design. I currently don’t own a pistol caliber carbine and like the AR platform. Though I do like the CZ Scorpion too. The CZ is a 9mm and has a folding stock option. All .45 is sub which is nice indoors suppressor or not. Choices a highlight of democracy.

    • “All” is a strong word 😉

      One of the biggest advantages to me that the Scorp has had over a pistol caliber AR is that it’s quieter. The ARs just open up too soon and there’s a ton of noise from the action. The ~1.4 lb bolt in the Scorp is good for enough of a delay that it’s noticeably quieter (and I think the bolt running in polymer might be quieter than a bolt and recoil spring setup in aluminum). I’m thinking the delay in this CMMG will make it pretty quiet, too, without a weight penalty.

  2. “Rotating to the side, rather than lifting up in the front, provides a more secure, reliable, stiffer interface” ……There’s a joke here about having a reliable stiff interface I just can’t find the right words.

  3. What is the buffer weight they use? The straight blow backs use a heavy BCG and a heavy buffer with different dimensions for the bolt hold open. Does this system allow the use of standard size AR buffers in the H2ish weight?

    • You can use any AR buffer, but they also provide buffers that can be inserted into the BCG to ‘tune’ cycling.

    • Yes I think it was just a standard H2 buffer, and the BCG is also a normal weight. As Jomo said, they are offering (not sure if it comes with it or if they’re sold separately) weights that can be affixed inside of the BCG to make it heavier to tune the action for +P ammo or suppressed shooting.

  4. Looks like the perfect home defense gun: ease of use by being an AR, .45 caliber which minimizes overpenetration but has stopping power, and parts commonality for spares. Too bad it’s not legal in my neck of the woods.

    • A real, full-auto one, I agree.

      One of the modern replicas … well, they look nice and shoot well enough, but they weigh a ton. I’m looking at selling mine because after the original “Whee!” at the range, it just isn’t worth the space in the safe for me.

    • My first thought – A Tommy gun for the 21st century! Even if it isn’t full auto I’ll bet it will send a mag dump down-range in a big GD hurry.

      Second thought – will it be available in 9mm? I’ve got 7.62, 5.56, 9mm, .38 Spcl and .357 already. Last thing I need is to go and spend a bunch of money on another load of ammo.

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