The Mag X – Make A P320 AR 15

Matador Arms is a small company producing some cool and original gear. Matador Arms is a Canadian firm and some of the gear they produce is aimed at the Canadian market. However, sometimes they just so happen to produce something that both American and Canadian audiences would love, and I believe the Mag X P320 is just that. The Mag X is a magazine block that squeezes into a Mil-Spec AR 15 lower receiver and gives us the capability to run SIG P320 magazines in our AR 15s.

Fits in the gun smoothly.

Of course, you’ll need a 9mm upper and a Glock bolt for this kit to function. They also suggest a heavy buffer. The combination of the 3 allows you to use a standard lower to run P320 magazines in a AR 15. The why is pretty easy, some people want to run pistol mags in a rifle platform and if you own a P320 this makes sense. If you were Canadian it makes plenty of sense as well. Canadians are restricted to 5 round rifle magazines but 10 round pistol magazines. There is no restriction on putting a pistol mag in a rifle either… so here you go.

X series 21 round magazines

From an American perspective, magazines aren’t cheap, and if you want a pistol caliber carbine it makes sense to have one that uses mags you’ve already sourced. The P320 is becoming quite popular and the magazines are available in a few different capacities. I went and wrangled two X series magazines that hold 21 rounds each for my conversion.

The Mag X Design

The Mag X is made from aircraft grade aluminum and has a black anodized finish. The mag well conversion is a rock solid piece of metal. It’s heft and feels well made. The Mag X has a built-in ejector and a magazine release. The Mag X inserts into a mil-spec lower easily and smoothly, like it was a magazine.

The AR 15 magazine catch holds the Mag X in place and is released via the magazine release. A lot of us have built the habit of hitting the mag release on an empty magazine and this would drop out the entire Mag X system. Matador clearly saw this coming and comes with a small bolt and washer that allows you to lock the Mag X in place.

Simple, but it works

With this bolt in the Mag X will not fall out of the gun. Now with a quick spin on an Allen wrench, the bolt is removed and you can eject the Mag X and go back to using a standard magazine.

Notice the Magazine Release

To actually release the magazine you use a large front paddle. You reach forward and press the latch backward and the magazine ejects with ease. You can grip the magazine and pull the latch rearward in one smooth movement. It’s quick and easy. The hardest part is retraining your brain to use the system versus a standard AR magazine release.

At the Range

I was a bit hesitant and was worried this system might be pockmarked by unreliability. It just seemed too simple to work effectively. Once installed, the bolt felt sluggish as I worked it back and forth. It wasn’t as smooth as normal. I applied some lube and it seemed to help a bit.

Very Simple, but very effective

The magazines were loaded to their full capacity of 21 rounds and this did make it hard to insert the mag in a closed bolt. Downloading one helps, or you can man it in there. Or load with the bolt open. You do you. I just manned it in there to see it would create a problem. Fortunately, it did not. The bolt racked rearward and went forward without issue.

Smack it home if you are loading a full mag on a closed bolt.

Outside of just testing the Mag X, I was also adjusting new iron sights. I took the first few rounds relatively slowly. Firing three rounds from the bench, adjusting, etc. In 12 rounds the sights were on and confirmed zeroed and I hadn’t experienced an issue.

So what’s next? A mag dump seemed appropriate, so I dumped the last 9 rounds into a steel target. Not a single issue in the first mag.

The Reload

I then went to reload and made a predictable mistake. I hit the mag release, confused myself for a second before fixing my brain-fart.

The front magazine release is easy and intuitive to use. It allows you to ensure the magazine drops free with a quick tug for your reload. I was carrying the next magazine in a mag pouch on my belt and attempted a speed reload.

Run It From the Pouch

This never happens to me, but I had an issue finding the mag well, or at least the the smaller hole in the Mag X. I bumped it on the back, and then banged the mag on sides trying to squeeze it into the mag well. Reloading a Mil-Spec mag well with a tiny pistol magazine is a little harder than you think. It’s a big readjustment to relearn the reload.

Releasing the Magazine

After two hundred rounds and roughly ten reloads, I had it figured out. In the first 200 rounds, I had one failure to fully eject. Since then, roughly another 200 rounds, I’ve not yet had another failure.

Ammo wise I’ve been using Remington UMC, the 8-dollars-a-box-stuff with brass casings. Its ran like a champ. The only other downside is there is no last round bolt hold open device. So you shoot until it goes click.

The Mag X In Practice

The Mag X isn’t for everyone, but it can provide you with a means to make a quick conversion to 9mm on your standard 5.56 lower. Alternatively, this is the only way I know of to make an AR (15, not an AR 10 or AR 18) feed from P320 magazines. For those seeking a higher capacity option, you can convert 21 round magazines to 31 with a plus 10 extension. Also, ETS showed P320 SIG mags at SHOT, with 30 rounders soon to be available.

It’s perfectly aligned.

The Mag X P320 is a very simple design that is well built and ultimately quite effective. SIG P320 magazines are bound to drop in price as the military begins fully adopting the weapon and aftermarket companies start smelling money.

Travis Pike is a former Marine Machine Gunner, a lifelong firearms enthusiast, and now a regular guy who likes to shoot, write, and find ways to combine the two. He holds an NRA certification as a Basic Pistol Instructor. is the world's Okayest firearm instructor, and a simplicisist when it comes to talking about himself in the 3rd person. Hit him up on Instagram, @travis.l.pike, with story ideas.

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