Imagine you’re at your local gun store, on the hunt for rifle ammunition. You notice something strange: two very different AR-15 ammo types (.223 and 5.56) that look virtually the same. But load one into the wrong AR-15, and you could easily turn your $2,000 rifle into a very fancy paperweight–or worse.

.223 vs. 5.56. How do rounds with such different names look identical? 

Sure, they are virtually indistinguishable to the untrained eye. And even an expert might be unable to tell the difference with just a passing glance. But make no mistake, these are different ammunition standards, and that difference is one you ought to know.

Read on as we discuss the two sisters of AR-15 ammunition.

.223 vs. 5.56: Some History Behind These Two Rounds

Of the two, the 5.56 is the oldest–so, technically, the .233 is its “offspring.” And before the 5.56 came the 7.62.

The 7.62 is the brainchild of NATO, an organization that sprung into being shortly after World War II. For at least a decade, 7.62 was the de facto military munition for armies spanning the globe. This was–and is–a hulk of a round with quite the kick and penetrating/stopping power.

However, the US and its allies were in search of ammunition that met the following criteria:

• Lethal: post-WW2, most soldiers wear armor that weakens the effectiveness of rounds
• Interoperable: soldiers should be able to exchange ammunition that works across standard infantrymen weapon platforms
• Affordable: on a mass scale, the ammo should be cheap to produce

The Transition from 7.62 to 5.56

7.62 was a recoil-heavy beast that, in large quantities, forced soldiers to truck in very heavy ammo boxes. Factories spent quite a bit more on brass and saltpeter to build these rounds. Despite the 7.62’s incredible killing power, it was overkill for all intents and purposes.

Thus the 5.56 NATO was born. 5.56 met all the criteria: it was cheaper, worked across weapon platforms, and still packed the necessary punch. It was such a slam-dunk success, in fact, that militaries the world over–US included–still use 5.56 on the battlefield.

So our army men, marines, and even Navy SEALs keep 5.56 close at hand. Kalashnikovs, however, remained with the 7.62. To this day, this Russian platform–from 47 to modern-day AK 100 Series–uses 7.62.

5.56 is intended for military purposes, but civilians can and do purchase it. So where does .223 fit in this picture, then?

Birth of the .223 Remington

The .223, or .223 Remington, is a creation of one of America’s oldest leading rifle and ammunition manufacturers. As we will discuss later on, the .223 is very, very similar to 5.56. Without the proper expertise, many wouldn’t be able to tell them apart.

Think of the .223 as the civilian version of the 5.56. The major difference, which we’ll discuss later in detail, is that 5.56 is higher pressure. .223 is lower pressure, but still works flawlessly with rifles chambered for 5.56.

Let’s talk one by one about the important differences between these two weapons.

Physical Differences Between 5.56 Ammo and .223 Ammo

Again, these rounds are hard to tell apart. But there is one surefire way that requires no knowledge whatsoever: checking the stamp. Flip the round over and read the imprint on the rim; you should see a clear .223 or 5.56 stamped there.

Further, the 5.56 sometimes has a slightly elongated neck to account for an additional grain of powder. This is practically impossible to note, though.

Of course, there will be no mistake when you buy these. Your box of new ammo–or one loaded with primed or certified once-fired brass–will have a clear label.

Just be extra careful never to get these rounds mixed up. You don’t want a 5.56 round to end up in a magazine with .223. You’ll soon see how this could be problematic.

5.56 Is Higher Pressure

Firearms live or die by how much pressure their rounds can produce. When you fire a round of any kind, it explodes, creating rapidly expanding gasses. The chamber contains these gasses, forcing them in one direction: out of the barrel.

High pressure can produce high velocities, which have a number of advantages that we’ll cover shortly. But one thing to keep in mind is that just because 5.56 ammo is AR-15 ammunition doesn’t mean that you can load it into any AR-15.

Rifle Chambering

Manufacturers “chamber” their weapons for a specific caliber. This means that the components are rated for that caliber, with little to no wiggle room.

Loading a round that is higher pressure into a weapon not chambered for it is bad news. This will stress the components to a degree they are not engineered to handle. The result is somewhat similar to spiked ammunition.

At best, loading 5.56 ammo into a rifle chambered for .223 will lead to issues like popped primers or extraction difficulties. At worst, your rifle may break and become inoperable. In some extreme cases, 5.56 could injure you when it ruptures the chamber and lower receiver.

You can fire .223 in a rifle chambered for .223. But velocity and accuracy will suffer to a marginal degree.

It Is a Higher Velocity

As a consequence of that high pressure, you get high velocity. High velocity, as you can imagine, impacts a bullet’s lethality, penetration, and stopping power. A good mixture of these things gives you the perfect trifecta of bullet performance.

Accuracy

Higher velocity also has a noticeable impact on accuracy. This is thanks to basic rifling physics: the faster a bullet goes, the faster it spins. Centripetal motion locks it into an even tighter line the more force you apply, and so you get better accuracy.

Bullet drop-off is also diminished. Bullets fly farther, at higher velocities. This is essential for soldiers engaging enemies at long distances such as 100 meters or further.

Naturally, 5.56 allows for soldiers to be more lethal, effective, and accurate on the battlefield. They could use .223, in theory. But 5.56 makes it easier to punch through cover, pierce body armor, and hit distant enemy targets.

It Requires Thicker Brass

To account for higher pressures, it follows naturally that you need stronger material. The base, walls, and neck of 5.56 are incrementally thicker. You won’t notice this difference in weight with your hands, but you will with a scale.

Having sufficiently thick casings is a big deal. If pressure is high, the cartridge could easily split and explode.

In developing their new 6.8mm 5.56 replacement, the US military contractors gave the cartridges a base with a different metal. This allows the ammo to be at much higher pressure without damaging the weapon or injuring the operator. In a similar way, 5.56 accounts for this with thicker brass.

The difference on the reloading table will be negligible. You won’t need any additional special equipment to reload your primed rifle brass. The only change will be that you add an extra grain of gunpowder during measurement.

It Has Better Ballistics

An AR-15 chambered in 5.56, and one in .223, won’t look or feel any different when you hold them. But one is superior in terms of ballistics: the 5.56-chambered rifle. Ballistic performance in the .223 is different enough that we’ve written a whole article on the subject.

Assuming identical atmospheric conditions, the 5.56 shoots at a higher velocity, with higher accuracy, and at a longer distance. This also assumes rifles with the same barrel length.

Normally, ballistics depend a great deal on trigger assembly, barrel length, and barrel-end modifications such as brakes and suppressors. But thanks to 5.56’s heavier grain, it shoots better without any of these adjustments.

So When Can You Use .223, and When Can You Use 5.56?

The obvious answer is to never load 5.56 into a rifle not chambered for it. .223 will work fine–albeit at reduced performance–in a 5.56-chambered AR-15. Check the stamp on your magazine well or the manufacturer’s guide if you are unsure.

However, there are other considerations beyond using rounds with their designed hardware.

Use .223 for Home and Personal Defense

In home defense solutions, you want to minimize collateral damage as much as possible.

Using full-metal jackets in an AR-15 is a bad idea. When fired, they’ll go through a home invader, walls, and eventually your neighbor or their kids. Hollow points or non-armored rounds are far less likely to stop in the intruder.

But to add to this, 5.56 is definitely overkill for home or personal defense. You aren’t going to be running up against ne’er-do-wells in military body armor that could stop a .223. Get .223 unless you’re in the military.

Use 5.56 for Target Shooting

5.56 has superior ballistic performance compared to the .223, as we’ve established. Granted, this is not a night-and-day difference, and will only manifest in long-range firing situations. But for something where accuracy is paramount–a marksman or target shooter–these tiny differences can amount to big ones.

Buy Your Casings from Diamond K Brass

.223 vs. 5.56: now you know the difference between these two landmark AR-15 ammunition calibers. While your AR-15 rifle will accept either, you should only load it with 5.56 if it is chambered as such. 5.56 has a higher velocity, performs better in terms of ballistics, and requires a specific, thicker brass casing.

Diamond K Brass supplies bulk orders of primed and/or certified once-fired ammunition. Get started with our 10,000+ bulk orders.