AR Testfire: The AAC Blackout .300

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From Gun Digest Book of the AR-15 Volume 4 by Patrick Sweeney:

The Advanced Armament Company has been making suppressors for some time now. In the process, they had to learn a whole lot about how rifles work. You see, simply hanging a “can” on the muzzle can do a lot to change the gas flow dynamics of a system. You keep the pressure higher, longer than the system was designed for, and that can cause difficulties.

The excellent flash hider and suppressor mount of the AAC Blackout.
The excellent flash hider and suppressor mount of the AAC Blackout.

The big one for 5.56 users is that a whole lot more gas than normal gets pumped back through the gas tube. So much so that the receiver can have the lube cooked or blasted, and a lot more powder fouling/soot builds up.

So when it came time to design a cartridge and build an upper to house it, they knew a thing or two about the job.

The cartridge is the .300 AAC Blackout, aka 7.62X35, made and loaded for them by Remington. It is an AR-magazine-length .30 caliber round that fits an unmodified 5.56 bolt, and as such the only real modification you need to make to your AR (or a new upper for it) is a replacement barrel. And while plugging new barrels into existing ARs can be fun, the real fun is in seeing what a maker decides they want in their own-built upper or rifle.

In order to make the deadline for this volume, I could not lay hands on a complete rifle. I was competing with every other writer out there, and a slew of paying customers as well. So, I had to wait until AAC did a short run of carbine-length uppers.

AAC uperThe 1/7 twist barrel is of medium weight (you really can’t make a lightweight, or pencil-barrel AR barrel, and do so with a .308” bore in it) and the 4150 steel alloy is black nitrided inside and out. The muzzle is threaded for the standard .308” bore AR threads: 5/8-24, so you can use any flash hider that would work on an AR-10 or other big-bore self-loading rifle. The one sent to me has the AAC Blackout® flash hider and combo suppressor mount on the end. The Blackout® is built to be a very effective flash hider, while also allowing a quick-attach system for the most-excellent AAC suppressors. As if that wasn’t enough, AAC makes the Blackout out of an unspecified aerospace alloy, to withstand the hard work of muzzle blast and the vibration of a suppressor in the end.

The barrel is plugged into a flat-top upper from Keyhole Forge, and marked on both sides with the lineage. One side is just “AAC” while the other side has “300 AAC BLACKOUT (7.62X35) ADVANCED ARMAMENT COMPANY” on it. Inside is a parkerized carrier and bolt, with a standard 5.56 bolt face.

blk-0010The handguards are where things get really interesting. Since the rest of the exterior is (as our British cousins phrase it) bog-standard, you could put any handguards you wanted on the .300 AAC Blackout upper. And I’m sure there are those who will insist on installing what they feel are the perfect handguards. But this upper came with the perfect handguards already in place.

It came with a Knight’s Armament URX II Mid-length forearm in place. Woo-hoo! While railed forearms can be a bit bulky (some can even be described as “porky”), the Knights are among the slimmer ones. And even with the rail covers in place, it is not too bulky until you start shooting with winter gloves on.

The front sight is hinged, and you only need press the button.
The front sight is hinged, and you only need press the button.

The really cool part of the Knight’s URX (besides being hard to obtain, and the same company that provides many of our high-speed low-drag military units) is the front sight. What, you don’t see a front sight on it? That’s because it folds down. And when folded, it appears to be just another section of the upper rail. Really, it is so low-profile that if you didn’t tell someone there was a sight there, they might mount a light or laser over it. And as a final bit of coolness, the Knight’s sight has its own thumbwheel elevation. Best to zero it and paint-mark it, in case one of your buddies decides to play with it in a moment of boredom.

AAC BlackoutThe AAC upper fit just fine on a cross-section of my rifles and lowers, so I didn’t have to dedicate it to any one of them. The feeding was flawless, and the ammo I had (at this time, I can only lay hands on the subsonic, 220 grain open-top match load) worked without fail.

Accuracy was top-notch, and you would not have any problems tagging a deer in typical woods distances, or a sentry at “across the clearing in the moonlight” distances. Actually, the 220 grain subsonic load is a lot more accurate than just across the clearing, but the trajectory is quite a bit to deal with. If you really are planning to use it at more than 25 yards distance, you would be well-served to find a ballistics program, calculate the trajectory, check it at the range, and keep a printout with you when you are loaded.

One thing I liked about the AAC upper was that it came with an owner’s manual. The corrective actions pages are good, as they tell you correctly that most of the problems are solved by unloading, cleaning and lubing your rifle. However, they still instruct the reader that the gas rings have to be turned so the gaps don’t line up, or the rifle will short-stroke. Alas, this is not the case, but it is very difficult to get such things out of the collective consciousness, once they get lodged there.

But the rest is good info, and the upper is primo. I just wish they wouldn’t use an SBR as the demo rifle in the photos. Each time I see it, I have to fight back the urge to consider moving to a friendlier state.


The ammo I had available that was real-deal, honest-to-god .300 AAC Blackout was Remington 220 OTM subsonic. However, the chambers are close enough that I had to test, because I know you guys will. I had on hand Hornady .300 Whisper and Cor-Bon .300 Whisper ammo. In the Hornady, I had the 110 V-Max and the 208 A-Max loads, and from Cor-Bon I had 125 JHP self-defense rounds.

They all worked just fine. The velocities they delivered were right in line with other rifles of the same barrel length, and the groups were on the point of aim and as good as you’d expect from top-notch ammo makers.

I think what we’re going to see from the short .300s in the future is a lot of reloading experimentation going on. Everyone out there with one or the other is going to load up, test, report and advocate their loads.

As long as you’re using an upper or rifle as top-quality as this one, you won’t get bad results.

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