MEAN Arms ExoMag 9mm Conversion Mag

Ammo prices are down from the shortage prices a few years ago. That doesn’t mean that they’re cheap, but some ammo is definitely more affordable than others. 9mm is about as cheap as  you can get in centerfire ammunition, and it might make you wish you’d picked up a 9mm AR.

If you have a rifle caliber AR-15 and want to drop a 9mm upper on it, you can always get a mag well adapter that uses pistol mags or Colt SMG mags. The adapters run anywhere from around $70 to a couple hundred bucks and then you still need mags, unless you already have some on hand. There’s also the issues of reliability with a conversion and ease of swapping your gun back to its original caliber when you want to. If you want to bypass all of that, an easier solution is to use the ExoMag from MEAN Arms.

But First, the EndoMag

MEAN Arms isn’t new to the 9mm conversion mag game. They’ve been making EndoMag conversions for a while now. The EndoMag is a drop-in conversion kit for Magpul Gen 2 or later PMAG’s that let you use 9mm in your existing magazine. Simply disassemble the magazine, pull the spring and follower and replace it with the MEAN unit. The EndoMag comes blocked to 10 rounds, but you can cut the “plug” to allow it to hold 20, or 30 rounds if your state allows it. Converting your existing mags is as fast as swapping out the spring and follower. 

Make sure you do use Gen 2 or later mags though. Initially I dropped the conversion in a Gen 1 mag and had feed issues. When I swapped out to a Gen 2 mag the issues went away. 

The EndoMag conversion has an ejector built into the mag, which is important for a 9mm conversion. Most dedicated 9mm AR’s have the ejector located in the lower. Since you’re using these mags in a rifle caliber lower, that ejector isn’t present, but MEAN puts it right on the magazine. Endomag conversion kits cost $29.99 and you need donor Magpul mags to work with.

Enter the ExoMag

If you like the idea of the EndoMag, but would rather have a dedicated magazine, then the ExoMag is what you’re looking for. These mags are made from scratch as 9mm mags. They still fit a regular rifle mag well, and are the same dimensions as an AR mag. That means that you can still use AR rifle mag pouches and carriers.

One thing I like with the ExoMag is that it is visually different from a rifle caliber magazine. Since the 9mm is much shorter than a 5.56 it only takes up a portion of the magazine width. MEAN skeletonizes the rest of the mag. This lets you know at a glance that you have a 9mm mag. On the EndoMag conversions I wrapped mine with tape so I could tell quickly which were converted to 9mm. You don’t need to do that with the Exo’s.

The first Exomag release is the big 40 rounder, and that’s what I had on hand to test. There will be 32, 20, 15 and 10 round mags available later. I’ll be honest, I’d have rather MEAN started with a smaller mag, as the 40s are pretty long. And honestly. I was a little skeptical on the reliability as problems seem much more common with the higher than normal capacity mags. But I was definitely willing to give them a run through. Exomags are priced at $35 for the 40-round mag and progressively dropping in price all the way down to just $20 for the 10 round mag.

Test Platforms 

I used three different guns to test both the Endo and Exo mags. All three started out as 5.56mm SBR’s. On one I pulled the upper from my H&R 635 clone. The next I used the Bearing Delay Upper from MEAN Arms. This one used a slightly different version of the ExoMag since it has an ejector built in to the bolt. This negates they need for one on the magazine like the other conversions.

For the last one I use my Spikes Tactical 9mm upper. For the haters in the peanut gallery, yep my Spikes is still rocking a Keymod handguard. It’s an older gun and it works, so I don’t mess with it. I think I still have three older SBR’s with Keymod. 

Anyway, aside from swapping the uppers, I needed to use the heavier buffers from the 9mm PCC’s as well. Being a blowback system the 9mm AR’s need a heavier buffer to cycle, so you have to swap out your rifle buffer when you move to 9mm. Unless you use the MEAN Arms Bearing Delay upper. MEAN designed that one to be a one for one swap without needing to swap buffers since it isn’t a blowback system.

Range Time

With converted guns in hand, I headed to the range. As a matter of fact I hit the range with the test guns a number of times over the summer. The MEAN Endo and Exo mags engage the bolt hold open of your AR lower so operation is exactly the same as your rifle caliber AR. Being that the mags are the same dimensions as a rifle mag, reloads feel the same as well, which is nice for continuity of training. 

In addition to my two uppers, I also used two uppers from a buddy of mine as well. He has a Foxtrot Mike FM-9 carbine and a home-built SBR. With my lowers and the five uppers I ran at least three hundred rounds through my set of 3 EndoMags and three Exomags. Reliability was 100% on each range session. 

We had a good mix of ammunition as well. From crusty surplus ammo to modern defense ammo, and both FMJ and hollowpoint loads. Bullet weights ran from 115 up to 147 grains. The MEAN mags presented and fed everything with no issues whatsoever. Despite my concerns about the 40-round mags and reliability, that didn’t prove to be an issue either. I think my skepticism of mags over 30 rounds comes from 5.56 AR mags, and I generally stock to 10-, 20- or 30-round mags. Although I do have a few Magpul 40-round mags and they do run, even though I rarely use them.

Durability seems as good as any mag. I let the Exomags drop to the concrete or gravel, depending on where I was shooting, when I reloaded. No issues presented themselves. They also rattled around around in my ammo cans and remained loaded between range sessions.

The ExoMag Advantage

Swapping to 9mm is easy with the ExoMag. You can use your existing lower with no modifications other than swapping out the buffer tube. You don’t need to deal with an adapter that adds expense and complexity to your rifle. Training is simplified since you’re using the same profile mags, and same operating principles as your AR in its original rifle caliber. 

If you have a surplus of PMAG’s then the EndoMag conversion may be a good option for you. But if you’re buying from scratch, I’d give the nod to the ExoMag. It’s a dedicated 9mm platform that you can tell at a glance is made for 9mm. It’s also cheaper to buy the ExoMag than it is to buy a PMAG and a conversion kit. You can order the 40-round ExoMags right now and put in a pre-order for the lower capacity versions. I plan on grabbing some lower profile 20-round magazines when they’re available. If you’ve been thinking about adding a 9mm upper to your existing AR and had hesitated not knowing what mag system to use, then definitely check out the ExoMag from MEAN Arms. It’s an easy and reliable solution to your problem.

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