300 Blackout Ammunition Compared to 5.56 NATO/.223 Rounds ~ An In Depth Report Part 3

300 blackout SilencerCo Osprey 45 SilencerShop Jim Grant
Changing your favorite AR-15 to 300blk is as simple as swapping the barrel. Plus, many pistol caliber cans can safely shooter subsonic 300 blackout like this SilencerCo Osprey 45 provided by SilencerShop.com IMG Jim Grant

USA – -(Ammoland.com)- I’ve heard the 556 v 300BO debate characterized as a Ford v Chevy comparison.  As if both were very comparable.

There might have been a small part of me that could have entertained that notion as a true thing before I researched and wrote Part 1 and Part 2 of this article series.  But there is no foundation for a Ford v Chevy debate left in my mind at this point.

The 556 and the 300BO are two completely different animals. 

If you really think about it, the only reason the 300BO exists stems from the desire to conjure up a cure for what was lacking in the 556.  By rights, these aren’t the same beast at all.  But, there is room for either and hopefully both in your collection.  I’d say if you have the disposable income to do both, you certainly should.  They both have different purposes though, so let’s see how they perform.

300BO vs 5.56mm Performance

I wanted to compare these two as closely as possible in the places they were most likely to overlap.  If you haven’t read the previous two installments in this series, you should.  They form the foundation for what I decided to do in testing and why I chose a 10.5” configuration.  There are things the 556 does better than the 300BO.  The inverse is true as well.  So, crossing the gap where they are similar is the way for me to go.  Other benefits of each are well established.

I decided to use two LMT MRP uppers.

LMT MRP .300 Blackout Chrome Lined AR-15 Barrel - 10.5"
LMT MRP .300 Blackout Chrome Lined AR-15 Barrel – 10.5″

The 556 is a unit I use often around the house and shop.  It’s a tad heavy for my liking, but I’m really confident with it. I’ve trained a lot and practiced with it extensively, and it never fails.  Yet, anyway…  I had several MRP uppers that were hollow, so I dropped in one of LMT’s 10.5 300BO barrels, set the headspace, torqued the barrel in, which takes nearly 30 seconds, and set up the rest.  I decided to use one lower in common among them, so as to remove other variables.  I used one of my own Controlled Chaos Arms lowersYes, I’m biased.  I’m running a Geissele Hi-Speed fire control trigger group and a pistol grip plenty big enough for my XXL mitt.  So, these uppers are operating on the same buffer, spring, etc. in terms of their gas system components found in the lower receiver group.

There are plenty of cans to choose from, but I remembered that years ago I bought a YHM QD can for a 300BO build that I never brought to fruition.  So I pulled it out of the box.  It had those spikes hanging off the front of it that are great for tearing up your pant legs and your soft case interiors.  The lathe made quick work of that nonsense.  While the cans aren’t the same, I’m not too worried about that.  I used Lancer L5AWM 30 round magazines.  I usually do.  There are many that are great and I use a lot of mag maker’s products, but if you can truly show me a better magazine than the L5AWM, I’ll use them.  The sights weren’t identical, as I used a set of LMT folders on the 556, and a set of YHM folders on the 300BO.  However, they were similar aperture sizes, so iron-sighted shooting yielded good results.

I spent time shooting at 25yds, 50yds, and 100yds.  I didn’t feel a need to go beyond that for the comparison and illustrations I wanted to make.  We know what each of these can do at a greater range.  The up-close-and-personal matters more in this case.  Could you use a 300BO for black bear?  Yes.  Could you use 556 for black bear?  I wouldn’t.  But if you were defending yourself, it’s better than a stick I reckon.  That’s the ethical hunter in me though, not the terminal ballistician in me talking.  I default to catastrophic potential wounds in hunting applications every chance I get.  For self-defense, halting a threat in an efficient manner isn’t exactly the same.

The more you shoot these two the more the idea of apples and apples goes out the window.  It isn’t possible.  We’re not talking about Red Delicious and Granny Smith apples here.  We’re talking about Red Delicious apples and Black Diamond Watermelons instead.  I used 62gr FMJ 556 ammo from my buddy Elliot, at Farro’s Lead Farm.  I used Gemtech 187gr subsonic (predator projectile) and also some Gorilla 150gr (Sierra FMJ) for the 300BOThe only reason I used two different types of 300BO was to illustrate its capabilities for hitting hard and remaining quiet at the same time.

You can see by looking at the 300BO that they’re both sleek and should feed easily.  While the black tip of the 187gr stuff is a dead giveaway, it is hard to notice just how much more bullet there is compared to the 150gr 300BO.  There’s a bunch more projectile seated into that case than is represented externally.  Both ran like a top.  But there was a distinct difference in sound from the subsonic ammo.  Sooooo quiet.  I loved it.  This is truly where the 300BO shines in my opinion.  The ability for the 300BO to run so well in an AR15 system with a short barrel and nearly everything the same with the exception of the barrel, all while truly quiet, is proof folks at AAC in conjunction with Remington Defense hit their mark.

I enjoyed plenty of accuracy from both.  With iron sights, I enjoyed anything from 5moa to 2moa as an average.  I had no stoppages with either.  I can tell you seating a completely full magazine into a lower with a closed bolt upper is a chore with either of these chamberings, so dumping one out and running 29 isn’t something to be upset with.  I’ve never broken anything doing it, but you have to really slam your mag home if you want to run 30.  I’m not sure it’s worth it.  During range time, fine, maybe, but I still prefer to train the way I intend to hunt or defend.  During a hunt or sparing life?  Not a smart move.  Stick with what is likely to avoid the most calamity.  That’s rule #1.

Both of these ammunition types ran somewhat clean.  But you have to understand that when you run a suppressed rig, especially one set up to run with or without a can, that some build-up and “dirty” parts will result.  I don’t worry about pistons too much.  There are true needs for them in certain short-barreled applications, but in 10.5″ with these two calibers, a well-built AR15 should work fine between suppressed and unsuppressed operation.

Both were accurate.  Both functioned well.  Neither gave me cause for concern.  I shot steel mostly and didn’t worry about terminal ballistics.  Why?  Because we know what they can do.  I didn’t mess around with high magnification scopes and attempt accuracy tests measured in thousandths of an inch.  Why?  Because I don’t care.  Both are capable of doing precise work, but that depends on lots of things – pairing the right load with the right barrel while being driven by an accomplished marksman.  I can quantify for you what I’m capable of, but this will vary among you all.  Some of you could easily best my greatest day, and some won’t get close to ever catching up with me.  So, I’m concerned less about seemingly arbitrary accuracy displays and far more about practical nominal outcomes.  If you can’t pick up either of these and nail a grapefruit at 100 paces via iron sights each time you grab a weapon, it’s on you, my friend.  The fact is, you should be able to do so with a tennis ball most of the time.  Both the 556 and 300BO are capable of this in the 10.5” configuration of a quality weapon.


  • We know the 556 is better at distance.
  • It looks like the 300BO has an edge close-up.

In AR15 short-barreled configurations (10.5” and below), I see nearly zero cycling problems with the 300BO in my shop.  The terminal ballistics are similar in shorter engagements.  Recoil isn’t a problem in either chambering.  The 300BO is the king of the hill for truly quiet suppressed shooting.  If you add these up, some might say the 556 is good for medium and long-range and the 300BO is great for short ranges.  But there are still several things you need to ask yourself.

How much are you going to shoot and what is your availability of the ammo you need?  We’ve seen some buying cycles in recent years that prove to me too few people are prepared for a rainy day.  And when it’s pouring outside you better have access to what you need or have it properly stored in bulk.  Think about that.  I have a 300BO 10.5” loaded with predator ammo in a suppressed rig at my disposal around the house and farm, especially for after-dark instances.  And I have a 556 10.5” BRN-180S, which I wrote about in 3 other articles here, here, and here, as the vehicle gun that travels with me all over.  There’s a clear and convincing reason for both.

That concludes my three-part report on the BLK 300 vs 5.56/223 I would love to hear what will you choose and why in the comments below?



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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I own both. A 5.56 in a 16″ barrel, and a .300 in an 11.5″ barrel. I like the .300 and have set it up a Home Defense Gun. Running the 220 gr Sub Sonic JSP’s it expands good in coyotes, so I think it will do fine with 2 legged predators. The .300 I run with the Vortex Venom 3 MOA Red Dot, along with BUIS. The 5.56 I’ve set up for a little further out. I do have a SIG Romeo Red Dot if I need to bring it inside 100 yards, but past I prefer the 4-12… Read more »

Boris Badenov

IF I were to live in a free state and not a wanna be Communist one and IF I were to have a 300BO with say a 10.5″ barrel from PSA with a Linear Compensator on it and it seems to run what the heck ever I ran through it from 110 gr to 240 gr Sonic or subsonic, I might tend to agree with the author but…I don’t have one so I can’t say much.

Last edited 11 months ago by Boris Badenov
Knute Knute

Good to see the author knows these two rounds are two completely different animals. I’ve chosen a 300BLK in a braced 8.5 inch, and a 16 inch 5.56. Plus a triangle hand-guard SP1. 20 inch pencil barrel, but that one is my favorite. The 16″ M4gery is the heavy 1 in 7 inch barrel, and its pretty heavy. Heavier than it should be. The Blackout is light and handy, fast to transition, but does run out of steam at about 300 meters or so. The SP1 is good at most everything, but does suffer from group scatter as the barrel… Read more »