This article proved tougher to write than the other articles I’ve written so far in my State Your Case series. Many of the arguments that I found worked for the others didn’t quite work here. Today we’re taking a look at two rounds for the AR-15 platform that have been in quite the rivalry in recent years with no end in sight: the .300 Blackout and .223/5.56mm.
To begin, we’re going to consider this a discussion on the AR-platform. There are bolt actions, single-shots, full-auto, and even pump actions made to chamber these cartridges, but the vast majority of people shoot them in an AR-15.
The real benefits of both rounds come from the AR platform, but that isn’t to say that the others are bad choices. As an example, I think that it’s unfair to give the .300 BLK points because it’s virtually silent in a suppressed bolt action firing subsonic ammo and say that the .223 is bad by comparison because it’s louder.
Side-by-side, the two cartridges share a great deal and a somewhat common lineage. .300 BLK is dimensionally similar in taper and case geometry to the .223, which is essentially its parent case. Brass for the .300 BLK can be formed from cut-down .223 cases. As a result of this, the only difference between .300 and .223 rifles is their chamber and bore. They share literally every other part, including magazines and bolts.
The reason that the .300 BLK is so successful is because it is a straightforward conversion that requires nothing but a barrel change on a standard AR upper. This is a big reason why rounds like the 6.5 Grendel, 6.8 SPC, and many others failed to gain much traction in the AR market. The .300 BLK just made more sense and was a quick and inexpensive upgrade that didn’t require special parts.
The other thing that accelerated the rise of the .300 Blackout was the availability of common bullets and loading components. The 2008-2016 suppressor boom saw the .300 BLK gain huge market share, and because guns, ammo, reloading components, and optics were readily available, it hit the sweet spot for many shooters. They could load their AR cartridges with the same bullets they used for their .30-06 or .308 if they wanted while using the same powder as their .357 Magnum.
The .300 BLK can be used with bullets as light as 78gr and has large as 240gr. It can be loaded supersonic at 2,800fps and subsonic as low as 800fps. It’s an extraordinarily versatile cartridge that performs well with virtually any barrel length from about 5” past 20”. These spectrums are a large part of why the .300 Blackout has taken the AR world by storm where others have failed.
The .223/5.56mm (we’re not going to go into detail on the minute differences here) is probably the single most common centerfire rifle round in America, and possibly the world at this point in time. The widespread, global acceptance of the 5.56mm cartridge means that there is a plethora of options available to shooters of any budget, from cheap M4 knockoffs to high-end precision rifles. Ammunition is made virtually everywhere and surplus loads are cheap and plentiful. High-end match ammo is all over the place as well as a variety of self-defense and hunting options.
The availability of .223/5.56mm weapons and ammunition make it a hard to ignore. A person today can arm themselves with a decent AR rifle, a good set of iron sights, a few mags, and 1,000 rounds of ammo for under $1,000. It might not be a pretty gun, but you can always change stocks or grips later.
Although the .223/5.56mm has some issues as far as terminal performance in combat situations, it has more to do with the bullets used than the gun. Typical, inexpensive FMJ ammo lacks in comparison to hollowpoints or soft points, which are only marginally more expensive, but will perform much better in a fight.
The bullets are fairly light, with most weighing between 55gr and 77gr, of course with some outliers on both ends of that, but they are generally effective inside 500-800 yards on man-sized targets. The issues with this round have led to some to try to design upgrades, such as the 6.5 Grendel and 6.8 SPC, but they all fell short in several categories when compared to the round they were trying to replace.
A huge benefit to the .223/5.56mm is ammunition weight. The light, high-velocity bullets can be carried in great volume in cheap, reliable magazines. This is a major consideration over .300 BLK, which can get heavy. A PMAG loaded with 30 rounds of 5.56mm weighs about 18oz, where a 30 round mag of supersonic .300 BLK can weigh about 22oz, and easily up to 30oz with heavy supersonic loads. Considering supersonic alone, you can carry six magazines of 5.56mm for the same weight as five loaded with .300 BLK.
For hunting, both the .300 BLK and .223/5.56 are limited to about 100 yards on most deer-sized game using the proper bullets. Despite what you hear today from the 6.5mm crowd, small bullets are still small bullets and a 5.56mm isn’t really ethical past 100 yards on a deer, but is fine on smaller game at longer distances. The .300 BLK is a great short-range deer round, especially for younger shooters and in states that allow suppressors for hunting. A large number of great expanding bullets exist for the .300 and many reliably open up at subsonic speeds. The .300 BLK is a national favorite for hog hunting.
So now it’s time to declare a winner. If ammunition supply and cost was not an issue, I would probably prefer the .300 BLK. I believe that it is a better round for more people and has a huge range of acceptable projectiles and end uses. The recoil is the same, if not lower, than 5.56, which means it is negligible. Overall, I think that the .300 BLK is one of the best rounds available for the AR-15, but…
I think that the winner of this debate has to be the 5.56mm. The factors of cost and availability are impossible to ignore, as are gear weight and effective range. While not as powerful at the muzzle as .300 BLK, the .223 shoots flatter at distance and allows more effective marksmanship training. I think that the mass public acceptance of .223/5.56mm guns and ammo mean that it, although it is wanting on a few angles, the one to have in the stable for a rainy day.