The Best .300 Blackout Magazines

How to pick the best .300 Blackout Magazines

The .300 Blackout is one of the more interesting calibers in recent years, officially approved by SAAMI in 2011, and born out of a need for a specialized close-combat round for special operations units, the .300 AAC Blackout has become one of the most popular chamberings for the AR-15 platform – and for good reason. 

Offering better ballistic performance and stopping power than the standard 9mm (the most popular subsonic SMG round) in subsonic AR setups, and you can run standard 5.56 magazines with any rifle chambered in .300 Blackout as the case dimensions are close enough to function in both.

Two AR-15 magazines with the black mag showing off a .300 AAC Blackout and the yellow mag housing a .223 Remington.
A black magazine running .300 AAC Blackout the yellow mag housing a .223 Remington. Note the difference in bullet sizes. A .223/5.56 NATO pill will run 55 to 77-grain bullets, while a .300 BLK starts at almost 100 and gets up to 220-grains.

While running a common magazine is convenient (one of the central features of the .300 BLK is you don’t have to change anything on your 5.56 AR beyond the barrel) there’s additional safety in dedicated magazines, which help mitigate dangerous cross-loading issues (chambering and firing the wrong ammo, causing a catastrophic out of battery detonation). 

To keep things as safe as possible we recommend dedicated 300 Blackout magazines. One mag for 5.56, one for .300 BLK – easy. Having magazines for rifles chambered in .300 Blackout will mitigate cross-loading, provide additional safety measures, and give you another reason to add to your kit. What’s not to like?

Additionally, some of our favorite manufacturers have crafted dedicated .300 BLK magazines. While these mags are, in many ways, identical to those 5.56mm variants, our recommendations will make it easier to tell them apart in your range bag, give you a sense for the best brands and features – all while keeping price point in mind.

The Magpul GEN M3 is a go-to magazine in any caliber and their .300 BLK mag is no different. Like its smaller-calibered brethren, the .300 BLK version retains all of the great Magpul GEN M3 features – like their crush-resistant polymer & aggressive front and rear texture. This generation’s impact and crush resistance, anti-slip and anti-tilt tech make them some of the most durable and best-designed magazines for rifles available.

These Pmags mitigate cross-loading by adding .300 BLK-specific features – like distinct rib design, rear texturing on the magazine body, and an easily-removable, slim floor plate. Additionally, they also have the GEN3 paint pen dot matrix, so you can denote .300 Blackout on the magazine itself.

The Magpul DOT matrix layout

Instead of opting for an aggressive front texture or specific ribbing, D&H keeps cross-loading at bay with a simple approach: include a visual indicator of the caliber on the magazine from the factory.

These magazines from D&H offer a 20-round capacity and a bright red follower paired with a specially-calibrated spring which improves follower/spring tracking and feeds the heavy .300 Blackout rounds more effectively than a standard 5.56mm magazine.

They’re made out of high-quality, black anodized aluminum for years of service and a solid lock into any AR mag well. The inclusion of the caliber on the magazine from the factory is nice and certainly looks more consistent than a DIY job with a paint pen.

One thing to keep in mind with aluminum magazines, they’re durable but can bend and dent rather than break (like polymer magazines might). With that said, it’s always a good idea to inspect the feed lips on aluminum mags occasionally to ensure they’re still in shape, especially after considerable use or they’ve been dropped.

Most AR owners have a lot of black Pmags laying around — it’s not uncommon to have a dozen or more at hand. Grabbing another Pmag and painting it for .300 Blackout might not be the best choice. Many shooters will dedicate specific types or brands of magazines to specific calibers. Breaking calibers out this way further prevents mix-ups and improves safety by making it easy to pair a specific caliber with the correct magazine.

Right in the same budget ballpark as the Pmag, these Hexmags have a hexagonal texture on the whole magazine, a red follower, and a matching red button on the bottom to view the floor plate. These simple touches make it less likely that you will misidentify the magazine, which makes these more than worth looking into. Using different mags for each caliber (like Hexmags for .300 BLK and Pmags for 5.56mm) will prevent cross-loading and simplify your range day packing.

Another way to avoid cross-loading — again keeping the feel of the magazine in mind — is to change its shape, and this 20-rounder from Magpul has a shorter length than the 30 rounder, making it easy to distinguish.

The 20 rounder offers the same great Pmag features, but measures in at a few inches shorter — so it’s smaller in-hand. Add some visual indicators like a specific caliber in the DOT matrix and this gives you a great solution without breaking from Magpul products if they’re your thing.

Keeping with the theme of changing things visually, many shooters use windowed Pmags for specific calibers like the .300 Blackout. We all have black magazines laying around, so changing both the color and adding a clear window to inspect the remaining rounds will help avoid confusion and give you an even more useful magazine for .300 BLK rounds.

One potential downside is these are traditional 5.56mm Pmags (which include the “5.56×45” notation) so if you’re not going to use the color of the magazine itself and a differentiator it’s would be a good idea to use a paint pen to clearly demarcate the intended caliber.

Again, the idea is to give yourself as many visual and tactile indicators of the intended caliber on the magazine, and we think these do a very good job at that. The window itself is also handy for keeping track of remaining ammunition.

Using 5.56 Magazines with a .300 Blackout Rifle

Again, you can certainly use .300 BLK rounds in a 5.56mm magazine without issue. If you choose to do so, it makes sense paint it a bright color or use a visual indicator (such as a paint pen or different colored follower) so that you know which magazines are which. Since the bullets are vastly different sizes you want a visual reminder to keep yourself from making a large mistake.

Conclusion

When considering dedicated .300 Blackout magazines, you have options.You can keep using your 5.56mm magazines, but identifying .300 BLK from 5.56 will be difficult without a means of avoiding cross-loading and the damage that can do to yourself or your firearms. 

With a little bit of forethought, this can be done with something as simple as a paint pen and a few minutes of your time.

A better solution is picking up some dedicated .300 Blackout magazines; our favorite manufacturers already make many options that will work well and are dedicated to .300 Blackout. However you solve for it – good luck at the range and stay safe!

Sources

  1. Magpul, Magpul Dot Matrix Diagram
  2. Sporting Arms and Ammunition Manufacturers’ Institute, Inc., Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Ammunition for the Use of Commercial Manufacturers, December 14, 2015
  3. C.I.P., 300 AAC Blackout, May 18, 2016

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MICHAEL CRITES is el jefe around here. He has spent more than 30 years shooting, learning about guns, and collecting firearms old and new. He’s tried his hand at 3-gun, trap, and distance-shooting, but ultimately enjoys ringing steel in the back 40 of his farm. His mission is to make guns and shooting accessible for everyone, and American Firearms is a passion project to help make that a reality.

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