300 Blackout vs 5.56

Not long ago, if a shooter wanted to buy an AR-15, their choice of caliber was like the color options on the original Model T Ford: one. There weren’t countless articles and influencers talking about ballistic efficacy or performance versus barrel length. If you were buying an AR, it was chambered in .223/5.56mm.

Now, current AR-15 buyers are faced with dozens of calibers and multiple operating methods to the point where it can be absolutely maddening. Just a cursory list of questions new gun owners have to face before making a decision can seem daunting – look at the abridged list below.

• Do you want a rifle-caliber or pistol-caliber AR?
• What kind of magazines does it feed from?
• Is the round an appropriate choice for its intended role?
• How expensive is the ammo?
• What kind of operating method is best?
• Is this gun/ammo legal in my state?

This is just a super short version of a list that could honestly span a few pages. And while I wish I had a two-sentence solution to every question a shooter might face, the reality is that the answers are complicated and vary on a case-by-case basis. So before you jump down the rabbit hole, that is, “What is the perfect AR for me?” I would recommend narrowing your focus. For example, let’s talk about the two most prolific AR-15 calibers available today: 300 Blackout and 5.56mm.

300 AAC Blackout vs. 5.56mm

Before we get into the head-to-head comparison, it’s important to understand the genesis and purpose of each caliber. Because it’s easy to get caught up in terminal ballistics, wound vectors, and ballistic coefficients, but to the layman nervously trying to buy their first rifle while an impatient line of customers grows behind him, this is all meaningless, confusing jargon. 

So, let’s start out with what each caliber is, what it isn’t, and why it was invented in the first place. And what better caliber to start with than 5.56mm – the OG AR-15 round?

.223 Rem / 5.56x45mm

In the aftermath of World War II, every major military was scrambling to adopt an intermediate power rifle cartridge like the 7.92x33mm fielded by the German military in their infamous STG-44 rifle.

Think of it this way if you’re hung up on the intermediate power portion. The primary rifle of United States infantrymen in WW2 was the M1 Garand. Made of steel and wood, the hefty rifle fired the very potent .30-06 round. This cartridge is best known today for being the go-to deer rifle caliber due to its excellent power and effective range. The .30-06 round is efficiently lethal (with proper shot placement) beyond 1,000 yards! 

But here’s the thing – most firefights take place within 100 yards. So, the extra power, weight, and recoil of .30-06 was mainly wasted. The Germans found that by shortening their primary round, 8mm Mauser, and chambering lightweight, select-fire weapons, their soldiers weren’t just as effective as before, but more so. Plus, the reduced size and weight of the round meant that soldiers could carry much more of the round on their person and in magazines.

The round also has substantially less recoil, making it a suitable alternative to a sub-machinegun when chambered in a select-fire weapon. From a logistics standpoint, this is a tremendous advantage. It means fewer calibers and, in the case of the M-16/M4, fewer rifles and parts to supply.

The US military’s first attempt at this was only half-hearted in the sense that they didn’t substantially reduce the weight or power of the round. And that’s where we get .308 Win / 7.62x51mm. 

The US fielded this round in the iconic M-14 rifle after the Korean War (1954). Still, by this time, the Soviets had already developed their 7.62x39mm cartridge and the SKS (as well as the RPD), with a few allegedly being fielded in the final days of the Korean War.

It wasn’t until 1964, with the formal adoption of the M-16, that the lightweight .223 Remington round would enter US service. This was the direct result of several large engineering companies working together to meet the requirements of a proposal set out by CONRAC or U.S. Continental Army Command.

CONRAC figured out what the Germans and Soviets had in years past –  lighter, smaller rounds fired at high velocity are equally as effective as slower, larger ones at realistic combat distances.

The new M-16/.223 Rem combo was so effective that early test shooters achieved an expert rifleman rating in boot camp at nearly double the rate of shooters armed with the .308 M-14. It wasn’t just because the new combination was very accurate but also because it doesn’t kick hard, and its 3,000 FPS muzzle velocity means shooters don’t have to change their point of aim to hit a man-sized target at 300 yards.

Now, it would be easy to stop there, but we should also address the elephant in the room -reliability in Vietnam. Yes, the first rounds delivered to our boys in Vietnam did cause malfunctions in the M-16. But there are some serious reasons for this issue. 

First, a group of accountants working under Secretary Robert McNamara changed the powder used in the cartridges. Initially, the round was to be loaded with a different powder than originally intended. While many have said that this powder was wrong for the round and suggested that it was insufficiently tested, the truth is quite different. 

According to the official inquiry penned by Representative Robert Ichord, it was a combination of poor QC from Colt with their barrels and poor QC of Olin, allowing for differing levels of calcium carbonate. The latter would cause excess fouling, and since the original guns fielded were touted as ‘self-cleaning’ and lacked a cleaning rod, these guns were neglected and coated in carbon build-up. 

Once these issues were cleared up, soldiers in Vietnam experienced only a fraction of as many malfunctions in the field. That said, there were some reports of poor ballistic performance. Still, many authors and official inquiries have suggested these resulted from the round’s poor performance when fired through the dense foliage of the Vietnam jungles, especially when compared to 7.62×51 NATO, which will zip through thin trees and bushes and remain lethal for several hundred yards. 

This is partially why 300blk was developed.

300 AAC Blackout

The story of .300 AAC Blackout, or .300blk, is a vastly shorter and simpler tale than that of the 5.56mm round, though it is a direct result of that round’s adoption by the US military.

With lessons learned in Somalia and the Gulf War, SOCOM wanted a new round specifically for special forces that performed better than M193 5.56mm from a shorter barrel. The round also had to function and retain lethality with subsonic loadings.

This was in direct contrast to the 5.56mm round, which relies almost entirely on velocity rather than projectile weight/size to defeat opponents. For example, standard M193 5.56mm ammo launches a 55gr projectile at around 3,200 fps, while supersonic .300blk fires a 125gr bullet at 2,200 fps. 

300blk uses a heavier, larger round because it’s less dependent on projectile velocity, which is dependent on barrel length. So if you’re a super secret squirrel door-kicker with a 10.5in M4 carbine, 300blk is going to outperform 5.56mm both because the heavier round will retain more kinetic energy at lower velocity and because powder used in this round is designed to burn faster and reach peak speeds earlier.

5.56mm vs. 300 Blackout

This brings us to the original intent of this article – which one should a shooter choose and why? As I mentioned earlier, it depends. But there are a few golden guidelines that can be used in most situations to determine which is ideal for you. So, we will list a few categories below and explain which caliber to choose and why.

Home Defense: .300 Blackout

Inarguably, if a shooter is looking for the ideal home-defense cartridge and is torn between these two rounds, 300blk is superior. It offers better terminal ballistics at close range and offers a wider variety of defensive loadings. Its lower velocity means it’s less likely to over-penetrate an intruder striking an unknown person or object behind them.

Personally, I would recommend subsonic loads coupled with a suppressor for two reasons: it doesn’t destroy you and your family’s hearing, and (with defensive ammo) these rounds tend to fully expand in a target, increasing the likelihood that a single round will incapacitate a target.

Hunting: .300 Blackout

While .300blk isn’t the best hunting round for North American game, it excels against whitetail deer and wild hogs alike. Shooters should avoid subsonic rounds in general for hunting as they can’t always penetrate deeply enough to reach an animal’s vitals. Also, the round is still an intermediate power cartridge, so consider it a lower-power .30-30 in terms of effective range. This means that you should limit your shots to 100 yards if possible.

Competition: 5.56mm

When it comes to centerfire rifle rounds, few are as affordable as 5.56mm. Combined with the projectile’s high velocity, this means hitting distant targets out to 500 yards, which is child’s play with either good eyesight or a decent LPVO. 

Not to mention that the round has very little felt recoil when fired from an AR-15 – so getting additional rounds on a target is limited only by a shooter’s skill. If you’re looking to get your feet wet in three-gun competitions, 5.56mm is the gold standard for a reason.

New Shooters/Learning to Shoot: 5.56mm

If a shooter is looking to learn the ropes and is dead set on a centerfire round, 5.56mm is king. Affordable, accurate, and low felt recoil means a shooter won’t learn bad habits like flinching when shooting a 5.56mm carbine.

Best of all, the high-velocity round can hit targets at distances well beyond the capabilities of the average shooter. So they won’t be limited by the round when learning to shoot accurately beyond average engagement distances. Whether you want to know the basics of marksmanship, how to use a gun in emergencies, or further your skillset and ring steel at a quarter mile, 5.56mm is the ticket.

Suppressed Shooting: .300 Blackout

Inarguably, 300blk is a vastly superior round to suppress than 5.56mm, namely because there are several subsonic loadings for the cartridge that are commercially available. The same isn’t true for the 5.56mm round since it relies so heavily on projectile velocity to damage a target.

Bugout / Survival: 5.56mm

Whether you’re hiking in an inhospitable backcountry or combing through the rubble after nuclear armageddon, 5.56mm is inarguably one of the best picks. Not just because the round has light recoil and is easy to hit targets at long range, but because it is so prolific that if you’re scavenging through a nuke-scorched Walmart or an abandoned police cruiser, you’re sure to find a few rounds and mags for your AR-15.

Verdict – Which Should You Choose?

Ultimately, the difference between 5.56mm and .300blk is one of physics. Do you want to hurl a lightweight projectile very quickly or a heavier round substantially slower? There’s no clear overall superior round for every situation. A similar argument has been made between .45 ACP and 9mm – except magazine capacity for the two is identical since 300blk’s parent case is 5.56mm. 

One thing is for sure: With modern defensive ammunition and proper shot placement, the differences between the two in a two-way gunfight are relatively minimal. And neither round nor the rifle/pistol it’s fired from will make you a competent shooter. Only training can do that.