300 Blackout Ammunition Compared to 5.56 NATO/.223 Rounds ~ An In Depth Report Part 1

5.56/.223 v. 300 Blackout
Energizer Battery v. 5.56 NATO/.223 (tall one on the right) v. 300 Blackout

U.S.A. –-(AmmoLand.com)- 300 v 556?  It almost sounds like a court case.  DC v Heller, Roe v Wade, etc.  The truth is, many shooters look at this as if it really is some kind of court case.  The problem with that thought is simple.  The jury is still out for many of us.

There are people who are fueling their flamethrowers as you read this.  The title alone will get their ire chain on the big sprocket and they’re reading to burn anyone on the other side of this discussion to the ground.  I have to admit, I have deeply held opinions myself.  But when it comes to the firearms industry, there don’t seem to be as many absolutes as you’d think other than safety measures.  There used to be plenty of black and white, but through industry innovation, continual sidestepping of law, codification, or ignorant rule, and the desire for niche performance, we have plenty of grey areas today.

When I was pitched the idea of writing about the 300 Blackout in comparison to the 5.56NATO, I assumed it would be a walk in the park.  I’ve built countless weapons for customers, my corporate collection, and my personal collection in both.  I’ve used both of these chamberings for everything from target shooting, training, and practice, to home defense, hunting, and carry.  Why would writing a series of articles be a problem?  Well, as I found out, making a choice of one over the other isn’t as simple as you’d think.

We should start at the beginning, or a brief history, of both in order to grasp their originally intended uses.  After all, I learned long ago in church that the most vital thing to seek in scripture is context.  If you don’t have the context of the subject matter, you’re in real trouble.

5.56 NATO/.223 Ammunition

62gr 5.56mm Ammo on Stripper Clips
5.56mm BALL XM185 Ammo on Stripper Clips IMG Jim Grant

There was a concept floating around in the 1950s that a small speedy bullet might be superior to a large slow one in terms of performance and also easier to use in fully automatic firing situations.  I’m not weighing in on which is better or worse.  I’m just offering the context.  You also need to consider that 1950 was a long time ago.  Both projectiles and powder have come a long way since then.  An opportunity arose to offer some new infantry weapons and along with a new platform came new rounds.  With irony, Stoner offered the AR-10 in 7.62x51NATO, which wasn’t ultimately accepted.  However, a parting gift was offered.  The AR-10 had a great impact and a scaled-down version loomed larger in the mirror.  This wasn’t as simple as laying it on the copy machine at work and hitting the, “Reduce by 20%,” button, but you get the idea.

The original testing design which used the .222 Remington was fine for testing, but the Stoner team agreed that the particular brass case wasn’t as tough as they’d like for the pressures they eventually wanted to utilize.  This gave way to the .222 Special and was later renamed the .223 Remington.  It was a tad beefier and a bit longer, so it could handle the pressure and feed pretty well due to length.  There were highs and lows with the .223 Remington, which we grasp as the civilian version of the 5.56.  But testing ultimately was favorable over a period of years.

Vietnam and Southeast Asian conflict had shown to be a significant spread of Communism, and opportunities presented themselves to field test the AR-15 rifle system.  Politics, roadblocks of all kinds, and practical concerns were raised.  The chief among them was, “Why change weapon systems and chamberings when we have a bajillion M2s and all the ammo we could need for them already bought and paid for?”  I don’t actually know if anyone said, “bajillion,” and I’m not certain “bajillion” is even a word.  But, it represents a lot.  And I believe it was a natural question to have asked and answered.  General LeMay was like a dog with a bone and had a track record for getting what he wanted – and General LeMay wanted the AR-15, thus the 5.56.  NATO eventually picked it up in the late ’70s and gave the 5.56 approval in 1980.  Officially, the 5.56×45 NATO, was adopted across many countries and many military branches.

The concept of a smaller and faster projectile coupled with a more controllable response when firing automatic-only took 30 years to be given the nod by the powers that be across the globe.  With lighter ammunition and various magazine configurations, the weapon system proved to be a true force multiplier as well.  If you were humping an M14 with 13 20-round mags at 21.5lbs, you could now carry an AR15 with 20 30-round mags at 21.6lbs – 280rds @ less than 22lbs became 600rds.  Engagement during WWII that was claimed to be 300yds and closer only could be extended with greater success.

There have been many considerations and configurations through the last 70 years.  I’ve built weapons in the chambering that were set up with ultra-slow twist barrels so I could send a customer out into a field of prairie dogs using 40gr hollow points.  I’ve built ultra-fast twist barreled uppers for target shooting that used 80gr projectiles.  The vast majority of rifle configurations fall in between and can swallow everything from 55gr to mid-70s and not a hiccup.  The rifle system, when properly understood, is truly versatile, simple, and very sound.

300 Blackout

300 blackout SilencerCo Saker ASR 762 Jim Grant
300 blackout uses a larger projectile than 5.56mm NATO, but still fits in standard AR-15 magazines, and works exceptionally well with sound suppressors. IMG Jim Grant

If it weren’t for such a versatile rifle, in and of itself, it would be hard to imagine the 300BO (300 Blackout).  We really must pay respect to the Stoner team, for there was a great idea realized that dramatically changed the world.  The sheer versatility the AR series offers us makes a lot of dreams possible.  I love that.

I’d heard of the 300 Whisper, and some years later I’d learn who J.D. Jones was.  But I didn’t realize until more recently the 300 Whisper was essentially the starting point for the AAC (Advanced Armament Corp) designed 300 AAC BLK.  That might sound kind of silly to you, but as you delve deeper into just how many chamberings there are out there in past and present alone, you begin to get the idea.  Go find a picture of the 8×35 Ribeyrolle.  Soak it up.  Then realize that it was developed for carbines over 100 years ago.  That’s WWI technology folks.  And most would take a quick peek at that and assume it was a 300BO.

To give you an idea of the timing present here, the 300 Whisper, which was never popular, was an early 90’s idea.  Fast forward a few years and there was a military call for something akin to the venerable AK-47 round, 7.62×39, for some limited applications.  Essentially the ask was this: give us something with better performance in terms of energy, without being too long or heavy, oh, and by the way, a subsonic version would be great, as the 9mm is good, but not great.  If you think about it, that’s a pretty tall order.  The AK-47 using the 7.62×39 was a great option, but unless you’re going to use a platform eerily similar to the Kalashnikov, you might not see success.  The steep angle of the 7.62×39 case in its design lends itself to the need for banana-shaped magazines and snag-free breeches and ramps.  Yes, we build, as do countless others, 7.62×39 chambered AR15 rifles.  But they often require some tweaks to assure users of peak reliability.  It wouldn’t be my first choice of options quite frankly.

When you have a suppressor building company with an eye on military sales giving time and energy to a project in league with Remington Defense, it isn’t a stretch to use a wildly popular and healthy system like the AR15, take its ammo, the 556, chop it, swage it, and stuff in a 30cal bullet.

Imagine you’re capable of using the existing weapon system, and all you have to do is change the barrel, pick a great and forgiving place to drill a gas hole with some system tweaks, monkey around with the projectile sizes and powder, and you’ll be a winner.  That’s horribly simplistic but somewhat outlines what took place that got us to today’s 300 ACC.

They really did come up with a winner.  I remember at the time it first started to take hold in the market, I had a friend, Thomas, who was enamored with it.  He was in his basement whacking off 556 empties like they were going out of style.  They looked extremely crude.  He’d then zip them through resizing dies, a Giraud trimmer he modified, and he was walking in high cotton.  I had no idea what he was doing was going to last.  But, he was at the range tearing up the course of fire and enjoying every minute of it.  I wasn’t able to realize the full 300BO potential, though, until I bought an upper myself and started to play with it.

At the time, suppressors weren’t legal in Iowa.  I had a Type 07 FFL with SOT II, and still do, so a safe full of cans wasn’t a problem for me.  It was for Thomas.  He made some subsonic 300BO and popped over to the shop one day.  He didn’t actually ask if he could try on a can but suggested I try it.  Of course, after I enjoyed the ultra-quiet shooting with a significantly louder “DING” from the steel than I was used to with my 556 carbines, I told him he should try on the beat-up YHM can I’d been using.  He was transformed.  I knew right then and there that not only was this a viable option in the market, but when cans were added, this thing had a real purpose in a relatively open band of use.  I also knew the moment suppressors were made legal in Iowa, that he’d have a half dozen on order.  …Which came to fruition a few years later.

The background and history of these two commercial chamberings are necessary.  If you truly think about it, each and every one of the boxes of ammo you’ll see on any shelf began life as a wildcat cartridge.  “Many are called, few are chosen,” was a bit of Matthew I was studying just the other day.  It tends to be this way with Wildcat cartridges.  There are so many different combinations of possibilities out there, that it truly boggles the mind when you think of all the possible outcomes.  But, very few make their way into familiar weapons and are marketed to the masses.  In our case, not every conception will run through an M4 flawlessly, use the same mags, and offer different potential outcomes.  That makes this ammunition pair mutually exclusive in some realm.  We’ll delve into the considerations of performance and applications in the next article as the jury continues deliberations.


About Michael Ware:

Michael is a Christian husband and father to two children. He owns and operates Controlled Chaos Arms, a premier custom weapons shop in the Midwest. He serves as Chairman of the board of Directors at the Iowa Firearms Coalition. The pursuit of truth drives him in research and his writing.

Michael enjoys shooting, hunting, and fishing throughout the Midwest and Rockies. An avid outdoorsman and tireless supporter of all Second Amendment virtues, he can be found in his gun shop, in a tree stand with his kids, or on Capitol Hill lobbying in support of Freedom and Liberty at any given time.

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WI Patriot

2 completely different rounds for 2 completely different purposes…and should never be any kind of comparison…

Knute Knute

But, since they are both based upon the same case and designed for the same wildly popular rifle(and are similar enough to fire in each others chambers, OFC to the detriment of those firing the 300BLK in a 5.56 chamber), comparisons are inevitable. Just the large number of 300 kabooms alone are enough to make comparisons inevitable. Since so many costly mistakes get made with it, such comparisons are a good thing, because the more people that learn to not carelessly fire the 300 in a 556 chamber, the better off we all will be. Comparisons will make at least… Read more »

Last edited 1 year ago by Knute Knute
Wild Bill

Most humorous!


I have to agree, would like to see someone try to put a 300 in a 223 chamber, jam would be at a strange angle dont think anything would hit primer, have seen a 223 in a 300 chamber did some damage I was suprised it did fire.extractor held it enough to fire case came out with a blown out shoulder like fire form for ppu,

Knute Knute

The Blackout is not SUPPOSED to be able to chamber in a 5.56…. but since the case is so much shorter, it all depends upon the ogive of the bullet. A short bullet with a steep ovige will probably stop before the breech block closes, so no discharge. But a bullet with a steeply angled ogive will go right up into the 5.56 chamber, and the bullet will set right into the shoulder of the chamber and lock up nice and tight. Except that the bullet won’t be in the throat, it’ll still be back in the shoulder where the… Read more »

Knute Knute

So I’m left to think that you two downvoters disagree with my statement: “Pull the trigger on that situation and: KABOOM!” ???????
This leads me to conclude that you think firing a .308 inch diameter projectile, down a .223 inch hole, using 30 tons of pressure right next to your face, is a hell of a good idea!
You trolls aren’t the sharpest tools in the shed, are you? Well, enjoy your impromptu facial surgeries! 🙂

Last edited 1 year ago by Knute Knute

I mark my 300 BO Rifles big time. And to get a 300 BO to chamber in a 5.56 you really have to make an effort.


Thank you!

Boris Badenov

I’m ammosexual, was a moderately early 300BLK adopter, before there was much information on it. Had a hell of a time getting my carbine length gas system to cycle, everything spec’d out but still no joy, then I found a lighter buffer spring and all was right with the world. I’d say I slapped together a rather short rifle and it ran perfectly but then I’d have to say it got lost in the floods.

Deplorable Bill

The 556 was designed as a maiming weapon and not so much a killing weapon. Given the right ammunition for the task at hand it will do both nicely. The 556 AR platform is a light recoiling round. It is surprisingly good at urban environs. It’s sufficient for yotes, deer, elk and the occasional terrorist, cartel operator etc. using the right ammunition. The AR platform is lite and accurate. This enables the user to carry that much more ammunition. Our basic load out was 720 rounds of 556, 200 rounds for the pig (M-60), 1 law, 1 claymore and 4… Read more »


I am still an m14 fan ,much longer reach and through tree capability. it is heavy but with a 762×51 I dont think It would be safe if it was lighter,you need to hold it down on auto. In urban overkill like a 50 bmg

Deplorable Bill

Yup a M-14 is a really good tool and it’s very difficult to hide from. Trees, cars and most buildings are mere concealment, not cover. I was issued a M-21, a glass bedded M-14, with a Leatherwood scope. Mason jars @ 1,000 meters were fair game. I did qualify with a M-14 but firing it in full auto mode accurately at anything more than 25 meters away was not possible.

Arm up and carry on


I’d say if you can’t afford both complete rifles in 5.56 AND 300 BO, buy an extra upper and swap them out. 5.56 for PRACTICE and 300 BO for self defense. The reason I go for that prefernce is becuase when I shoot a 12″ x 1/2 AR 500 gong and 100 yards the 5.56 goes PLING and doesn’t even budge the gong. The 300 BO goes THUNK and I can get the gong swinging! That tells me there is a lot more in the THUNK they in the PLING.


I LOVE IT! You KNOW we are going to see your THUNK and PLING “specs” mentioned in the future of firearms and ammo!


Failed to mention a big reason for the low adoption rate of the 300 Whisper is because J.D. Jones kept it a proprietary cartridge never sending it to SAMMI. Had he done so the Whisper would likely have been more popular.

Knute Knute

Hey, whatdayaknow! Someone else who knows about the 300 whisper! Do you also remember JDJ’s first try, the 30 whisper? Living in MT, next to Idaho, I’ve been following JD since well before the whisper series. Since the T’SOB scope mount for heavy caliber Contenders, to be exact.
Remember his .44 “Magmatic”? The fixed barrel, gas operated, multi caliber, autoloading pistol? I still want one to this day. Too bad it never left the prototype stage. I wonder what problem he ran into that he found insurmountable?


Thank you, Michael, for the article. I have wondered about this round.

I really wonder what it would be like to have a 243 in AR platform. If they made them, I would own a few. My wife can shoot it and not kill her shoulder, to me it’s just another pop gun and for some reason it is more accurate at longer distance than the 556 shooting a 100-grain boat tail hollow point which does a job on wooden 4×4’s much better than 72 grain in a 556.

Last edited 1 year ago by musicman44mag

You can get a .243 Win barrel for an AR10. Last year a YouTuber that goes by CRS Firearms did a build that he called the Body Armor Shredder. He was able to punch through 3/8 AR500 with a 55 grain ballistic tipped round.



I know I am late but thank you for the info.


You’re quite welcome. When I get around to building up my “spare” AR10 receiver set I’m most likely going with .243. Bet one of those would zip right through a blue helmet.


You can get an AR 10 upper from AR10 Parts in .243 and it uses .308 magazines. https://ar15parts.com/upper-assemblies/243-winchester-uppers-ar10-lr308/


I know I am late but thank you for the info and especially the link. Very helpful.


6.5 Grendel, 7.62x39mm, and 350 Legend are all available in the AR-15 platform and all kind on the shoulder. All with more impact than the 556


I like the 243 because it is gentle on my and my wife’s shoulder and I have a lot of that for her hunting rifle. I just like the accuracy, the power behind the little bullet and flat trajectory as well as range more than the 223. Thank you for the info.

Knute Knute

Those are the same reasons I like my .25-06! And my .270 Win. too, although now it’s not quite so nice on the old shoulder anymore. I can’t remember the last time I shot my .300, let alone the .338. I liked big when I was younger.

Wild Bill

Yep, that will happen to us all someday. But NOT today!


I had a 270 and it was for deer not elk. I went 7mm and finally shot 1,000 yards. I hit the target but not to my satisfaction. I am looking into 338 lapua now. Very expensive and I have friends trying to turn me towards 6.5 Creedmoor but I have a lot more homework to do.


My oldest son who lives in Alaska was wanting to go the Lapua route until reality hit him right between the eyes. On sale, four months ago, a satisfactory hunting round went for $4.00 apiece. I looked at him and said, “It would cost you at least $50.00, to sight the sucker in, if you’re lucky. Even with a good muzzle break…I am sure it would hit the shoulder hard. (I have never fired one, but seen a whole lotta pictures!) Besides, who would take a thousand yard shot at a moose or Grizzly? My 7mm mag. is more than… Read more »


I am so bored of 300 and 500 yard shots. I can actually hit a 12 inch gong at 300 yards with my 22LR. I have to aim about 5 foot high but I can hit it, LOL. That ‘s always a challenge and it really tells you who makes the better rifle and stronger ammo too. My Marlin tube feed outdoes my Ruger. As far as cost, I load my own and right now I am getting hit up by the neighbors to teach them how to load. When they find out how much the equipment is including powder,… Read more »

Wild Bill

May I suggest a Christianson in 6.5 PRC. Very accurate rifle, and not expensive.
The cartridge reaches farther and faster than the 6.5 Creedmore and similar low felt recoil.
I topped my with a 6-18 x40 Leupold real bargain glass). I zero’ed it to 300 yds. It reaches out to the far edge of our rifle range (1350 yds).


Interesting. I will check that out as I will with all suggestions. I will no buy until I m absolutely sur that I am buying what I need.

Wild Bill

A wise policy!

Knute Knute

If you like big(and don’t have my falling apart shoulder) and are willing to pony up the cash for a Lapua or a Cheytac, might I suggest one of my favorite calibers, the .378 Weatherby? You get the .375 bore size, which has a very good selection of bullets readily available, is good for almost any game on planet Earth, good ballistic coefficients for long range, and has factory ammo available. Although reloading is certainly preferable, both in terms of cost and for long range accuracy. Also it will fit in a lot of different bolt action receivers, and the… Read more »

Knute Knute

“Yes, we build, as do countless others, 7.62×39 chambered AR15 rifles. But they often require some tweaks to assure users of peak reliability. It wouldn’t be my first choice of options quite frankly.” I refuse to build anybody an AR in 7.62×39. The taper of the case means that to really be reliable, the magazine must have a large curvature, which means a straight mag well like the AR’s needs to give way to the “rock and lock”, system used by the AK, and others like the Ruger mini14. Yes, one CAN make them work in the AR’s mag well, but it’s… Read more »

Alan in NH

I built several 7.62×39 AR’s and success depends on the magazine. C-Products work fine, others maybe not so much. 10 shot mags all run flawlessly. So it depends what you want it for. Also built a 5.45×39 AR that runs great with most regular AR magazines loaded to 28 rounds. Your milage may vary.

Knute Knute

“Your milage may vary.” Yes, it almost certainly will. That’s the part I’m attempting to avoid. The inevitable failures when the mileage doesn’t meet the customer’s expectations. I prefer to avoid such pitfalls as much as possible by first off, clearing the way as much as possible. For me, this means avoiding things that I KNOW will cause me problems, like shoehorning a heavily tapered round into a too straight for its taper magazine. Not that it’s impossible. I just prefer to avoid the problems that will come with making that choice. IF I were a factory, though, that would… Read more »