The Best .300 Blackout Uppers

Who makes the best .300 Blackout upper receivers?

Despite all of the lasers, tech accessories, and modern features, the AR platform is more than half a century old.

Originally chambered in .308 as the AR10, Eugene Stoner made a rifle that was chambered for a round that was full of compromises, the 5.56 NATO.

To be fair, we certainly like the 5.56mm: it’s a capable round that’s lightweight, shoots reasonably straight out to about 500 yards, and has been getting the job done since Vietnam.

With that said, we’ve had 50 years or so to optimize the system, and that is exactly what has happened with the .300 BLK round. The .300 Blackout was engineered from the ground up for the AR platform – and it does not disappoint.

If you have ever fired an AR in 5.56mm indoors, whether a range or in some other circumstance, you know that it is, in fact, a seriously bad time for you and anyone north of the barrel in terms of sound, flash, and concussion.

So, in trying to develop a round that hits harder at short ranges, as well as suppresses supremely well, you’ll want to take a look at the .300 blackout. 

Quick List: The Top .300 BLK Upper Receivers

Palmetto State

For pistol uppers, Palmetto State Armory has put together a sweet offering here. This one has a short barrel that needs their flash can to get out in front of the handguard, but that makes it perfect for home defense or close quarters. We also love that they put irons on it from the factory. 

The handguard, as much as we like the lightweight, has enough material cut out of it that we expect great thermal performance, but possibly at the cost of your hands, so think about some gloves when shooting this one.

What we liked:

What we didn't:

Radical Firearms

For our second choice on the list, we’re going with the Radical Arms Assembled upper. It’s a fairly standard .300 Blackout upper, but with one thing that we like.

It has a 16” barrel. While that might seem like an odd choice for a pistol, it is a way to convert an existing rifle lower to .300 blackout without all of the time and hassle of ATF paperwork.

We do wish, though, that these would come with iron sights.

Sure, you can get your own easily enough and by now you probably already have an optic ready to go in a drawer at home, but still, it’s those little details that our experts appreciate. 

What we liked:

What we didn't:

Daniel Defense

Daniel Defense produces some of the best high-speed platforms to more than capable operators – like the U.S. Navy SEALs.

This upper from the folks at Daniel Defense is certainly no exception to their quality. The fit and finish are excellent, and the 10.” barrel is about the perfect length for a .300 blk pistol.

With the already short length here, we think the best application for this upper would be to add a short suppressor and use subsonic ammunition.

Doing that will let you shoot 300 blackout indoors without totally ruining your eyes and ears: this makes the DDM4300s a  great entry into this new caliber.

What we liked:

What we didn't:

Smith & Wesson

Smith and Wesson have been getting into the AR game really seriously in the past ten years, so it’s great to see them selling an upper in .300 blackout as well. This one is meant for mainly rifle configurations, and we think it would be especially useful as a hunting rifle when paired with a quality suppressor. 

One thing we might change out were it our gun is the handguard: it has a ton of room to mount anything up to and including the kitchen sink, but the square profile is kind of thick in the hand.

What we liked:

What we didn't:

Aero Precision

To round out our picks, we wanted something that would be especially suitable for a pistol built, and the Aero Precision M4E1 is awesome for that in the 8” barrel format. 

It comes with a flash hider, but we recommend putting a suppressor on it to increase overall length. At barrel lengths this short, there is the temptation to put your hand in front of the barrel or too close for comfort, so a suppressor hanging off the end might not be a bad idea.

With this one, you’ll be providing the bolt carrier group as well as the charging handle, but overall this is one of the best .300 blackout pistol uppers out there.

What we liked:

What we didn't:

Why the .300 BLK?

Two AR-15 magazines with the black mag showing off a .300 AAC Blackout and the yellow mag housing a .223 Remington.
While the .223/5.56 NATO (yellow mag) generally runs 55 to 77-grain bullets, the chunky .300 BLK (black mag) starts at about 100 and goes all the way up to around 220-grains. This makes for a slower, more suppressor-friendly round.

The short, stubby round, the .300 BLK gives you improved performance over the 7.62x39mm at 300 yards. And at close range, the 5.56mm, frankly, is an awful round. There’s a good reason that Colt made ARs in 9mm going back into the Vietnam era. Indoors and out of short barrels, the 5.56mm makes a ton of noise and even more flash, so it’s really not engineered for CQB or urban combat at all.

Of course, the 9mm approach is only a stopgap measure that lacks in stopping power at range. It also requires 9mm-specific components – and you still end up with a sub-par AR full of compromise (or more of a PCC). For military and law-enforcement applications, a .300 Blackout-chambered M4 is a marvelous sub-gun replacement, with a cartridge consderaly more effective than a 9mm pistol-caliber MP5. For home defense, the same thing can be said in a .300-chambered AR replacing pistol caliber carbines – lots more stopping power with little fuss.

In standard 5.56mm, ARs will hit peak burn out of about a 16” barrel, with 14.5” as short as you can go with a 5.56 barrel and still get performant terminal ballistics, complete powder burn, and a lack of a fireball.

Those longer barrels make them more cumbersome when it comes to close range applications like home defense.

Instead, we want a short-barreled rifle or pistol that, especially when paired with a suppressor or muzzle brake, can lead to a handy and quiet rifle that still makes more impact than a 9mm, and in most cases more than 5.56mm.

Tests by AAC way back in 2012 (and of course ballistics have improved since then) demonstrated that the .300 BLK could still be effective out to 440 yards– when fired from a barrel as short as 9-inches, making it ideal for use in AR pistols.

When it comes to a bad-breath-distance engagement, we want .300 blackout.

In addition to its performance characteristics, one of the major contributors to the .300 Blackouts popularity is its compatibility with existing 5.56/223 AR-15 rifle components.

Your bolt carrier groups, upper and lower receivers, magazines, rails, and the like work just as well with the .300 BLK as your 5.56 NATO rounds. Plus .300 Blackout-chambered AR-15 still uses the same magazines without a loss of capacity, i.e. a 30-round 5.56 NATO AR mag will still hold 30 rounds of Blackout. Just swap the barrel and gas system and commence pow-pow.

The circa 2011 Advanced Armament Company's .300 Blackout AR-15 platform
The circa 2011 Advanced Armament Company's .300 Blackout AR-15 platform, achieving impressive performance from just a 9-inch barreled SBR. (AAC Photo via Department of Defense)

What’s The Best Form Factor for a .300 Blackout?

For the .300 Blackout, shorter is better. The round simply doesn’t perform at range they way a 5.56/223 round. It’s a heavier, slower-moving round, but thanks to the .30 caliber bore, will burn its full potential in a 9-inch barrel.

That means that, no, you won’t be punching out targets at a mile. But, inside of 200 yards, you’ll be hitting well above the weight of a 5.56mm.

Because it moves slower, it’s also a lot quieter: this makes .300 blackout a great choice for a good flash suppressor, a silencer, or a muzzle brake. So, we recommend shorter barrel lengths that are excellent for close-quarters engagements making a .300 blackout rifle or pistol a great option for home defense. 

What do I need to know when picking a .300 Blackout Upper? 

First of all, a little legalese will be necessary here. Since .300 Blackout does best out of shorter barrels, we’ll be recommending AR pistols as final builds.

That means that the lower you put it on has to have been registered as a pistol when it was made and that you cannot put a stock or a forward pistol grip on it. But we all love a good brace!

Also, you’ll want to consider what muzzle devices you want to try out. Since we think a high quality .300 blackout does so well suppressed, we think a pistol upper with a threaded barrel is about the perfect way to get the best out of the round.

A .300 blackout pistol, with a suppressor, is still only about as long as an average AR15 without a suppressor, so it ends up a really handy package overall, which is one of the things that we like about the round.


With that said, all of the options on this list are good, and we think you could make a great pistol or rifle out of any of them: we recommend thinking about the parts you already have and what you want to do with them before making a purchase. With this guide in hand and a little bit of thinking, you’ll be well on your way to an excellent .300 blackout pistol or rifle.


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MICHAEL CRITES is el jefe around here. He writes about guns and gear.

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