History and Development of .300 Blackout vs 5.56 NATO / .223 Rem

AmmoLand writer Logan Metesh examines the history & development of .300 Blackout vs 5.56 NATO ammunition rounds.

History & Development of .300 Blackout vs 5.56 NATO / .223 Remington
History & Development of .300 Blackout vs 5.56 NATO / .223 Remington

U.S.A. –-(AmmoLand.com)- The AR platform is arguably the most popular one on the market right now. Primarily chambered for the 5.56/.223 caliber, the gun has been adapted to a variety of other calibers over the years, but none has gained wider acceptance than .300 Blackout. Let us take a look at the benefits & drawbacks of .300 Blackout vs 5.56 NATO ammunition rounds.

History of 5.56/.223

The genesis of the 5.56 and .223 calibers is the same as many other popular calibers over the years: it was driven by the military.

The era of the heavy-hitting battle rifle had come to an end. The M1 Garand and the M14 rifles were phased out and a new and radically different rifle – the M16 – was coming of age.

Colt Armalite AR15 Model 01 serial number 000106. (Courtesy James D. Julia Auctions)

ArmaLite’s new rifle design demanded a new caliber, and their initial intention wasn’t to reinvent the wheel. At first, they floated the idea of using the commercial .222 Remington, which was a popular varmint cartridge. Unfortunately, that caliber wasn’t up to military specs, and so they had to go back to the drawing board.

james sullivan
James Sullivan, developer of the 5.56x45mm round.

What emerged was a similar yet distinctly different round: the 5.56x45mm developed by James Sullivan, who had worked with Eugene Stoner on the rifle’s design. The cartridge was officially adopted in the US in 1964, and the “civilian” version, known as the .223 Remington, was soon put into production as well.

NATO, however, was not pleased with this new cartridge. Having only recently switched to 7.62x51mm, they were in no hurry to change yet again to another new round that they deemed inferior. Eventually, they relented, and in 1980 the 5.56x45mm cartridge became the NATO standard.

Both the 5.56 and .223 cartridges have proven themselves with the military and civilian markets alike. After almost 60 years of use, it’s safe to say that both are here to stay.

History of .300 AAC Blackout

A relative newcomer, the .300 AAC Blackout turned 10 this year, but it has accomplished quite a lot in just a decade. Work began in 2009 by designer Robert Silvers as a joint venture between Advanced Armament Corporation (AAC) and Remington Defense.

robert silvers
Robert Silvers (LinkedIn)

As the story goes, a military customer approached them in 2009 wanting to use standard M4 (AR) bolts and magazines that would retain a 30-round capacity, but fired a .30-caliber projectile. Work continued through 2010 and the cartridge was approved by SAAMI in January 2011.

The result was the .300 AAC Blackout, which stood on the shoulders of an earlier wildcat cartridge known as the .300 Whisper.

Even though .300 Blackout had military-minded roots, no organization has officially adopted it across the board. It has, however, become incredibly popular with AR enthusiasts who are looking for something a little different.

Benefits and Drawbacks of .300 Blackout vs 5.56 NATO

The biggest benefit of 5.56/.223 ammo is its prevalence. Well, at least until the ammo shortage of 2020 began. Whether you roll your own or buy off the shelf every time, there was no problem finding this caliber because it was in use by almost everyone, everywhere.

Run out of ammo at the range? No problem. The pro shop was bound to have boxes in stock. It’s not like you had run out of something obscure, like 10.15x63Rmm.

One of the biggest drawbacks is in terms of sound suppression. Using a suppressor with a firearm in this caliber will certainly bring the decibels down, but it really won’t make them “hearing safe.” And remember: just because you can tolerate the volume doesn’t mean it’s safe. Oh, and if you want to run it on a 7” pistol build? Ha! Forget about it! Better have that ear pro handy!

Benefits and Drawbacks of .300 AAC Blackout

The biggest benefit of the .300 Blackout is that it allows caliber diversity in the AR platform with minimal changes to the gun itself. All you need is a different barrel, and given the LEGO-like qualities of an AR, this is easily swapped out by popping two pins and slapping on a new upper receiver.

You can use the same bolt, same charging handle, and same magazines. If you’re into uniformity, you could outfit an entirely new upper with the same physical setup, just with a different caliber barrel. Pretty nifty.

Where the .300 Blackout really shines, though, is when it is used in conjunction with a suppressor. Subsonic loads are impressively quiet when shot from an AR outfitted with a suppressor. Even with shorter barrel lengths, it still does a great job at keeping the decibels down without sacrificing overall performance.

One drawback to this cartridge is the cost. Even though it’s similar to the 5.56/.223 in many aspects, they part ways at price. You’ll definitely pay more per round for .300 Blackout.

300ACC Ready Uppers at your Favorite Gun Shops

“300ACC Danger Will Robinson”

The biggest drawback to this cartridge, however, is also one of its biggest benefits: shared gun parts with 5.56/.223 cartridges. But since the .300 Blackout was designed to fill a regular AR mag to its full capacity, careless loading or a lack of oversight could lead you to grab a mag full of the wrong ammo.

In .300 Blackout vs 5.56 NATO the limitations of the .300 BLK are, again, primarily based on capacity and bullet weight.
In .300 Blackout vs 5.56 NATO the limitations of the .300 BLK are, again, primarily based on capacity and bullet weight.

It gets worse, though. You can chamber a .300 Blackout round in a 5.56/.223 barrel, but you absolutely cannot fire it from that barrel without the gun experiencing a catastrophic failure and putting yourself at risk of serious physical harm.

As a result, you’ve got to keep an eye on what rounds you have in what mags, and what upper you’ve got installed on your lower receiver.

.300 Blackout vs 5.56 NATO Which One Wins?

To be completely honest, I’d say it’s a draw. They’re both great for their own purposes and have their respective places. I think picking a true winner depends on personal application. If you’re all about shooting suppressed, .300 Blackout can’t be beaten. If you’re a casual AR enthusiast, then 5.56/.223 is where it’s at.

That said, variety is the spice of life and you shouldn’t have to “Sophie’s Choice” your firearms, so why not own both?

About Logan Metesh

Logan Metesh is a historian with a focus on firearms history and development. He runs High Caliber History LLC and has more than a decade of experience working for the Smithsonian Institution, the National Park Service, and the NRA Museums. His ability to present history and research in an engaging manner has made him a sought after consultant, writer, and museum professional. The ease with which he can recall obscure historical facts and figures makes him very good at Jeopardy!, but exceptionally bad at geometry.

Logan Metesh

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I enjoy having both. My .300AAC is an SBR, so it’s set up as a home defense weapon with sub sonic rounds. As for keeping the mags apart, I buy P-Mags for my 5.56 Carbine and Hexmags for the .300. Makes it easy to differentiate between the two.


Exactly what I did AND my hexmags are grey and the pmags are black.

WI Patriot

Been loading and shooting 300BLK since almost the very beginning, LONG before commercially available brass…use to cut and form my own 300BLK brass…

Ryben Flynn

I did that at first until commercially made brass became available.


I have a Dillon case trimmer with a 300 BO set up and make my own out of LC brass that works great! The problem now is the insane price of 1x fired brass. It used to be about $40-$50 per thousand now some folks want as much as $150. I have about 5000 rounds of 300 BO anyhow.

Last edited 1 year ago by CourageousLion

Component prices are way out of whack. Bullets are about the only component with a modest price increase. OF and new Brass is through the roof. Propellant prices are way high, and locally, we’ve not seen any primers since May of 2020. Thought I had enough to get through the shortage, but I’ve had to cut back on shooting, as my stockpile diminishes.


spelling errors no I didn’t shoot 6.5, iT made a steller record. Not me.


Great article. … But it caused me to digress to research the “10.15x63Rmm” which somewhere down the “rabbit hole” brought me to RCC Brass (https://www.rccbrass.com/). Which, in turn, for many reasons made me hopeful for the return of this country to “greatness”, individual success and freedom to innovate … among other thoughts. … As does all the math, science, technology and innovation that goes into firearm and ammunition development, evolution and manufacture. … Just wanted to share those thoughts. Excerpt from 4th para. under “Design” (https://en.wikipedia.org/wiki/Mauser_Model_1871) – “Serbia adopted a more up-to-date version of the rifle in 1881, the M1878/80,… Read more »


The 5.56 round is anemic when it comes to muzzle energy compared to the 300 BO. At 100 yards the 2000 FPS 300 BO with a 150 grain bullet develops 1332 foot pounds of energy while the 55 grain at 3000 FPS develops 1099 foot pounds. 5.56 was designed to put 3 people out of commission on the battle field. The victim of the shot and the two others that are needed to remove him. At least that is how the story goes. If you’re a MAN, you would use an AR 10 instead of an AR 15. .308 vs… Read more »


problem was the guys looking after wounded were ours , i had a m14 you could cut dow a tree with it


Switching between supersonic and suppressed subsonic, the noise reduction is amazing.

Country Boy

Was .300 Blackout made in an attempt to compare/exceed performance of the AK-47’s 7.62×39 mm cartridge? I always figured it was. Was it?


No, there’s no ballistic info it’s comparable. 7.62 is closer to .30-30, I explained below that the original .300 was invented to get around the rules in 3Gun and allow the AR15 in competition. Nonetheless, they refused it. READ THE POST COMPLETELY. TL;DR: After AR’s were allowed in 3Gun .300 died on the vine with SSK working it as a suppressed round, and AAC simply renamed it to get some market share. It worked. When the AR was allowed in Service Rifle, same story, .30 cal slipped in the ranking and AR’s lead. Old news. If you want the history… Read more »

Country Boy

.300 Blockout is predated by two other cartridges dating back into the days of SOF magazine, and their First Invitational 3Gun Match at Chapman’s Range in Columbia MO. I attended that match as a spectator and enjoyed the hosted events. During the match I was in a group observing behind the line when a competitor approached us and, having a captive audience, explained he had prepared a .300 AR15 to compete in the match. It would have been per the rules, however the intent was to prohibit the AR entirely as back then Real Men Shot .30 Cal Battle Rifles.… Read more »

Xaun Loc

“The biggest drawback to this cartridge, however, is also one of its biggest benefits: shared gun parts with 5.56/.223 cartridges. But since the .300 Blackout was designed to fill a regular AR mag to its full capacity, careless loading or a lack of oversight could lead you to grab a mag full of the wrong ammo.” NO… That is not the biggest drawback to this cartridge! The biggest drawback is a poor design that should have never been approved by SAAMI at all. The fact that every round of .300 Blackout is just a KaBoom waiting to happen is due… Read more »


While I understand your point, I disagree. There are many calibers on the market with that issue of being accidentally loaded into the chamber. 20ga vs 12ga right off the bat.

If one’s not paying attention to every detail, they’ve no business owning a firearm IMHO.


Remington ammunition is crimped and is full of powder, so the projectile can’t be pushed back. But yes, handloaders or less experienced commercial ammunition companies can make ammo that is possible to incorrectly chamber. Remington took care to not do this.


I’ve see a few of the 300 BLK at the range, but have never gotten an anser to a curious question: from shence came the name “blackout”?


mumble…black ops..mumble,mumble..suppressed…mumble..tactical…cool…mumble..target audience…
Or 300 Whisper was taken, 300 Fireball sounds dated, and 300-221 sounds boring. What I’m trying to say is that AAC marketing just needed a cool sounding name.


From the MMA world.

Old Vet

Just one minor error in your article, the .223 is not the same case length as the 5.56. If you have a very tight .223 chamber it might cause you pressure problems shooting 5.56 rounds in it….just a caution.


Just a caution? If you are using book loads for either there is no way you will develop enough pressure to cause issues by using a 5.56 round in a .223 rifle. And the .223 Wylde takes care of the “problem” and is why I use that chamber in my personal builds.

Xaun Loc

NONSENSE! Yes, Old Vet, there is some truth to the “pressure” issue — but not much — and there is absolutely no truth to your claim that there is any difference in case length. The case length of SAAMI approved .223 Remington and milspec 5.56x45mm NATO cartridges are exactly identical. There are some minor dimensional differences (mostly due to how the measurements are specified) .223 Remington Bullet diameter 0.224 in Neck diameter 0.253 in Shoulder diameter 0.354 in Base diameter 0.376 in Rim diameter 0.378 in Rim thickness 0.045 in Case length 1.760 in Overall length 2.260 in Case capacity 28.8 grain H2O (1.87 ml) 5.56x45mm NATO Bullet diameter 0.224 in Neck diameter 0.253 in Shoulder diameter 0.354 in Base diameter 0.377 in Rim diameter… Read more »

Ryben Flynn

Another nice thing about 300BLK is the 16″ 1:8 twist barrel I have has a pistol length gas system which allows for cycling on heavy subsonic rounds. I have subsonic 5.56 rounds for my other AR but it is a single shot deal as I have to manually chamber the next round. For varmint hunting with a suppressor it is no different than using a bolt rifle.


Except loading them in the chamber manually is a heck of a lot slower then any bolt gun.

Ryben Flynn

No. They are in the magazine and I just have to rack the charging handle again. That’s what I meant by manually chambering the next round.


It’s quite the stretch to state that Silvers “developed” the blackout. The blackout was outright stolen from JD Jones, who did all the work long before his design was stolen.


Is that who developed the Whisper rounds?


The military groups considered using the Whisper, but rejected it as unreliable. 300 BLK, at least in the form of ammunition developed be Remington, solved the issues with 300 Whisper.