The AR world is absolutely massive, and you can chamber an AR in everything from .22 LR to .45-70 Government. The AR is often adapted to function in calibers it was never designed for shooting.
While that’s cool when it happens, what’s even cooler is when rounds are designed specifically for the AR platform.
One such round is the .300 Blackout. The .300 BLK has easily been the most successful new caliber in the last 20 years.
Read on to see how to get your standard 5.56 AR-15 ready to use .300 BLK.
Summary of Our Top Picks
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Editor's PickBallistic Advantage .300 BLK Uppers
The 10.3" BA upper is the basis of my truck gun build.
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Runner-UpAero Precision M4E1 Assembled Upper Receiver .300 BLK
Another proven company for complete uppers.
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Another Affordable OptionRadical Firearms .300 AAC Blackout Upper Assembly
Another affordable option if you have your own BCG or CH.
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Table of Contents
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Why the .300 Blackout Succeeded
The .300 BLK became a behemoth in the industry because of its direct compatibility with existing AR-15 rifles since it is compatible with almost every standard 5.56/223 AR-15 part.
This includes magazines, bolt carrier groups, upper and lower receivers, rails, buffers, buffer assemblies, stocks, etc. Really, the biggest change is the barrel and the gas system.
Other than that, it’s a standard AR-15.
This makes it possible to convert your 5.56 AR-15 into a .300 BLK AR-15 with nothing more than a swap of the upper receiver.
That’s it.
You can use the same mags, same BCGs, etc.
Why You May Want a .300 Blackout Upper
Besides the easy conversion between 5.56 and .300 BLK, the .300 BLK does a lot the 5.56 can’t.
First off, it’s a very versatile load with projectiles weights ranging from 110 grains to 220 grains. The 110-grain rounds are supersonic, and the 220 subsonic.
A subsonic round is much easier to suppress and much quieter when suppressed. The .300 BLK also reaches peak ballistic potential from a 9-inch barrel.
The 5.56 requires a 20-inch barrel to reach peak ballistic performance.
I won’t dive too deep into the 5.56 vs. .300 Blackout debate because we have an article on that.
In my opinion, the two rounds are designed for different tasks, and having both simply opens up your options.
What I will do is point you to a few of the best .300 BLK upper receivers so that you can make your transition to this wonder-round.
Best .300 Blackout Barrel Length?
This question comes up a lot…and the answer varies depending on your end use and if you’re using a suppressor.
We asked Clint Hanson, the founder of Ballistic Advantage, and his go-to barrel length is 10. inches for reliability.
The 10.3-inch length is “not too short and not too long from an all-around/fit every human size standpoint” because you have to figure in the handguard and potential suppressor length.
Once you go under 8 inches or so, you can run into cycling issues since the .300 BLK is a low-pressure round.
So if compactness is the name of the game…make sure you have a suppressor to add some backpressure and also enable you to run a longer handguard.
“Every length has a problem it’s solving, but the 10.3 inch is the go-to and most versatile.”
Best .300 Blackout Uppers
1. Palmetto State Armory
PSA makes a huge range of items for the AR-15 platform and, for that matter, the AR-10 also.
One of the many things they cover is the .300 BLK in uppers of all sizes, from 7.5-inch barrels all the way to 16-inch barrels, with every standard size in between.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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No matter what kind of .300 BLK build you want to create, you can find the upper for it from PSA.
Short little pistols? Check. SBR? Check. Rifle? Check.
PSA is also, generally, one of the most budget-friendly options.
2. Ballistic Advantage
I love Ballistic Advantage 5.56 barrels (full review) for the right mix of performance and affordability.
This time I checked out both a 9-inch barrel and a complete 10.3-inch BLK upper recommended by Clint Hanson.
I chose the 10.3-inch Hanson barrel factory upper to be my trunk gun, where I valued reliability without needing a suppressor to add back pressure. The length also gave me enough rail real estate to put on lights.
I had initial problems with using an upgraded WMD NiB BCG, but once I switched back to a mil-spec BCG it ran everything like a champ.
From steel-cased Wolf range ammo to brass supersonic and 220gr subsonic rounds.
Coupled with a LAW Tactical Folder, it fits nicely into my small trunk safe.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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My editor’s pick recommendation for a do-all .300 BLK upper.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
For my suppressed home build, I went with a 9-inch Modern Series barrel for something slightly shorter but still reliable. It’s been flawless with all different types of .300 BLK ammo.
Check out all the .300 BLK Complete uppers here or just the barrels if you’re looking to build your own.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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What’s your take on BA?
3. Aero Precision M4E1
Aero Precision is one of the best companies out there for modern, high-quality AR components.
The M4E1 in .300 BLK comes available in 8-, 10-, and 16-inch barreled options.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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A 10-inch barrel on an AR pistol or a short-barreled rifle is perfect for the .300 BLK. The uppers all feature different-length handguards that accommodate the mounted flash suppressor.
Aero makes gear that works, and these uppers are perfect for your next .300 BLK build or to convert your 5.56 rifle. We also love their 5.56 uppers – check out the review.
4. Radical Firearms .300 Blackout Uppers
We all have a budget to live and die by, and recognizing that, I’d suggest any of the .300 BLK options from Radical firearms.
These budget-priced uppers lack a BCG and charging handle, but they’ll take any standard AR BCG and charging handle.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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These uppers range from 8.5-inch barrels to 16-inch options. Radical firearms also produce their uppers in a wide variety of configurations.
These uppers aren’t the fanciest, but they work.
They are mil-spec, and all feature flat top uppers, forwards assists, and threaded barrels. Prices range, but each option is affordable and thoroughly modern.
My personal favorite is the 8.5-inch upper with an MLOK rail. It’s short and sweet and perfect for a .300 BLK pistol or SBR. The M-LOK rail is fantastic and provides more than enough room for accessory attachment.
5. Brownells BRN-180
Want to go a little different? Enter the BRN series, which is based on the AR-180 series that didn’t have a buffer tube but instead went with a short-stroke piston.
That means if you went with an under 16-inch barrel (which you pretty much gotta do with a .300 BLK), then you can get a folding brace for a super compact AR.
My choice is the 10-inch .300 BLK upper that we built for a super nice truck gun.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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We also combo-ed it with the BRN lower which gives you Picatinny rails for use with your favorite brace or stock (if you go the SBR route).
And be sure to snag a bufferless Picatinny end lower receiver.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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Check out our full review of the 16″ 5.56 version.
.300 Blackout Safety
I do want to note one thing before you run out and get a new .300 BLK upper – you NEED to be careful when switching between uppers or even when you have a dedicated .300 BLK rifle and a 5.56 rifle.
You see, .300 BLK can chamber in most 5.56 barrels; however, if you try to shoot it – your barrel (and sometimes more) will literally burst.
Explosively.
As you can see in the image above, bad things can happen when you load the wrong cartridge into your rifle.
Make sure you keep ammo and mags separate.
Personally, I keep them organized by using different color mags – FDE and black for 5.56 and Olive Drab for .300 BLK. I also double and triple-check things before loading a mag into the rifle.
Final Thoughts
With suppressors and SBRs being all the rage, the .300 BLK continues to grow. The ammo price continues to drop, and upper receiver options are everywhere.
These are just my favorites and represent a very small section of the market. I’m one man and couldn’t possibly see each and every upper out there. Knowing the industry, there must be some amazing options on the market I simply haven’t seen.
Check out more calibers and everything AR in the Ultimate AR-15 Resource.
What are your favorite .300 BLK upper receivers? Anything that makes them stand out? Need a dedicated optic for the .300 BLK drops? Check out our Best .300 BLK Scopes & Optics.
42 Leave a Reply
Literally the worst list I’ve ever seen lol. You think that Aero and PSA are making the best .300 BLK uppers?
300 HAM'R leads the way. It's everything 300 Blackout supersonic wishes it was.
Anyone have a top 5 recommended, 300 blackout stripped upper with the focus being lightweight and gas reducing? This would be for an 8" barrel.
To keep gas out of your face, you may want to choose one of the new flow-through, 3d printed suppressors from OSS/HuxWrx. Sig is attaching these to the new Army rifles running 6.5. However, subsonic 300blk tends to be pretty good about letting the operator breathe, depending on manufacturer. I'd also recommend going a little longer, ideal length for gas burn is 9", so 10 or 10.5" are perfect, and that keeps gas out of your face too.
Any ole 300blk pistol upper from PSA at that length will work just fine. If you want to get a little pickier, go with an adjustable gas block or one that's long enough to allow you to slide an adjustable gas gadget under the hand guard and that pokes out a little to let you adjust it. It may be on the heavier side because they like heavy barrel profiles, but there's Faxon with a pencil barrel if you want it to lose weight.
I have recently joined an Anderson lower with a upper receiver that I got from Bear Creek armory for something around $200. It carries a silencer central can and my property is super densely forested very few clear long shots so this is absolutely perfect for me. Just make sure and meet ATF's guidelines for AR-15 pistols. A 10 and 1/2 in barrel is okay.
The only key here with ATF's standards is a collapsible brace that maxes out at 14" from end to trigger face. Otherwise barrel length doesn't matter, when you start with a "pistol lower" kit.
Pretty old article, all of the mentions of keymod give it away, as the industry has moved to the magpul standard m-lok. Can we get an updated for 2022 article? 300 seems to be heating up again and with the eform form 4, suppressors (and calibers that are easily suppressed) are also popular.
Hey Chris, we're slowly making our way through updates on older articles. But I will make sure to put this on the list to get to it sooner rather than later. Thanks!
Please tell me the make and name of the two AR-15 300 blackouts shown in the picture with the description "Suppressed .300 Blackout"
I like the way these two set ups look.
Please send me the specs (including the name of the suppressors)
We found the image on the Wilson Combat website several years ago, they do not seem to be available anymore. I have no information on the specs, sorry.
Those are Radian Weapons Model 1 AR's.
I have a Radial 8.5" 300blk and it is a nice tight fit on a Areo M4E1 (No need for tension set screw) It shoots straight out to 50yds/ 1.5" group free standing, bench rest 100yds / 3.5" group but I blame the shooter. That is far as train with a 8.5" it is a CQB set up. Headspaced checked out good. People talk down about Radial like they are junk. News people Radial pistol uppers are good to go for what they are designed to do. The only down side would be the barrels are 4140 so I would guess they won't hold up to high round counts. But at their price point I can buy a complete upper for the cost of a barrel from other name brands.
My first ar 15 was on of their rf15. And its held up great. My only issue is with the buffer tube and and exploding gas tube but both are my fault.
This list definitely should be updated to include gas piston systems. Primary Weapons Systems sells a complete upper exclusive on Brownells that is competitively priced compared to the others on this list, but you get a far superior action. The model is MK1 Pro.
So what I'm gathering from this is, I can use a 5.56 BCG as well as a charging handle in a .300 blackout upper, correct?
Correct!
Roger That
Yup. And a 5.56 lower too.
Interested in a one-stamp, integrally-suppressed blackout upper. Any u guys can recommend or recommend staying away from? Thx!
here's just what you're lookin' for bud....
http://www.pewpewtactical.com/go/aero/aero-precision-300-blk-upper/
daniel defense
No DDM4 300S?? I have one of these and wouldn’t think twice about buying it again. Only drawback is they force you to buy a BCG and charging handle with an upper only purchase...since I already own a DDM4 V7 Pro I didn’t much like having to pay the extra money for what I already owned.
I saw the 300BLK fire from the 5.56 chamber rife, What would happen if you fire a 5.56 from a 300BLK rife
Catastrophic failure!!! That is what will happen!!! You can use the 5.56/233mags with the 300blk and the bcg, but that's it, so eaither buy a upper chambered in 300blk or swap barrels.
shooting 5.56 in a 300blk will not explode - but your guess is as good as mine where the bullet goes . . . if it doesn't engage the rifling it doesn't fly straight
What handguard/upper is the bottom most picture with the 2 rifles?
Both rifles are Wilson Combat, I'm not sure if those exact ones are still made though.
Have been looking at all the AR variations and would like your thoughts/advice on a particular package I'd like to build - .300BO, 16" 1:8 barrel, gas piston, and side-charging upper. Is this doable without special gunsmithing? If so, any recommemdations on the best components?
What FDE upper is in the top pic?
what FDE upper is in the top pic ?
I agree extreme care and good organization are a necessity when dealing with uppers in multiple callibers ... but a .308 chambering in a .224 ? I haven't tried it, but it seems implausable.
The bullet does not fully seat in the chamber, it just seems like it does due to the exact lengths involved. It will still fire. This is a well-documented issue with .300 BLK and 5.56.
Here are some pictures that more clearly show it happening: Cut-Away and article, https://uploads.tapatalk-cdn.com/20160501/d175a60f384060cfabc4c555b349fd4f.jpg.
Enjoying your AR reviews. May I suggest: reviews of side-charge-handle AR uppers. Much more ergonomic for target shooting and hunting - anything from sitting or prone positions. Plus ... no nose bleeds from slapping yourself in the face when your hand slips.
I have purchased a couple of .300 blackout upper receivers from MAS Defense. One pistol and one rifle. I have to say that I am impressed with the quality of their products. The pistol upper has a 10.5" barrell with a 12.62" free float hand guard. There is a flash can tucked neatly inside the handguard. This pistol runs flawlessly. Same story with my 16" rifle. I haven't had any issues with the 416 stainless barrel. Awesome products by an awesome seller. Check them out!
Anyone offering a left-handed 300 AAC upper?
I haven't seen any, sorry. I suspect the market for that is just too low.
Stag Arms may . I have one of their left handed ARs.
I just built a Classic Firearms (Bear Creek Arsenal) .300blk 16" stainless barrel with an Anderson upper. Very accurate and pretty cheap. That is my two cents. I would do it again the same way if I did it again.
I built mine from Anderson Mfg. upper and lower at a price cheaper than any previous AR Build...very satisfied with the quality of each component.
I built a .300 in a A2 dissipator configuration, using a pistol length gas system. A2 receiver and stock. Very smooth and the accuracy is excellent with just irons.
As usual, great article.
I bought the 8.5" Radical Arms upper for my SBR. I chose it both for price and the handguard was the 1.5 inch slick tube. On a DD lower this thing is GREAT. With YHM Phantom flash adapter and suppressor all you hear is the bullet hitting the berm. Great investment all around!
My wife purchased a bear creek Arsenal .300 blk for my 36th birthday this past December 14. I was elated!! I’ve added upgrades and she’s never failed me not once. I noticed that the rifle feeds better using tapco magazines but I’ve had some success with my hexmags as well. I run Remington umc in both 120 and 220. The rifle performance is amazing. No failures of any kind. I pick up boxes of 20 at Walmart for 15$ and some change. Can’t beat it. I made some half inch thick targets of steel at varying design and man the rifle makes em sing!!