The most common question surrounding the .223 Remington and 5.56 NATO is “are they the same thing?”

The answer: yes, but no. In reality, they’re slightly different — and the differences matter. These two rounds share a singular history and have more in common than not. However, the subtle differences create a very important distinction, one that can mean the difference between a great day at the range or a trip to the hospital.

In any case, the .223 Remington and the 5.56 NATO are both incredibly popular rounds that should have a place in any shooter’s ammo cabinet. Let’s look at the difference between these two rounds to get a better idea of how to use them.

.223 Load Development

In brief, the .223 Remington was developed in partnership with the military to replace the 7.62x51 NATO (.308 Winchester) as the standard infantry cartridge. The 7.62 is a hard-hitting battle rifle cartridge that is difficult to control in full-auto fire. Its bulk adds a lot of weight to a soldier’s loadout. To make troops more accurate and effective while reducing their gear, the .223 was designed to fire a 55-grain bullet at high-velocity and relied upon speed to cause trauma and hydrostatic shock instead of the brute force of the 7.62. The “.223” designation is in reference to the bullet’s diameter, although it’s a bit of a misnomer because the bullets carry a diameter of .224”.

After some tweaking and plenty of testing, the 55-grain .223 Remington was given its stripes and renamed per its bullet diameter and case length: 5.56x45mm NATO (the 5.56 being the metric equivalent in millimeters of .223”). It earned the NATO moniker because it is an official cartridge of the North Atlantic Treaty Organization, the global force whose members are bound to watch each other's back in the event of an attack on any one member country.

Since then, scads of other 5.56 and .223 rounds have been developed for different purposes, with a variety of bullets. All yield an excellent blend of performance characteristics that make them incredibly versatile rounds. For instance, the M855 green tip is a 62-grain penetrator round with a steel core. The 77-grain is made for precision work, but it tends to run more expensive.

Difference Between 5.56 and .223 Brass

With both of these rounds, the devil’s in the details — especially regarding their cartridge cases (colloquially as “brass”). The 5.56 and .223 share virtually identical exterior dimensions and are almost indistinguishable to the naked eye. You’ll need a scale to tell them apart beyond the headstamp because the 5.56 is a tad heavier. Externally, the only difference between the two is a slightly more aggressive shoulder on the 5.56 relative to the .223.

The 5.56 also operates at a higher pressure than the .223 — we’re talking 10,000 psi more. Now, this is nothing to spit at. It’s the main reason why there’s a distinction between the two rounds. The 5.56 brass is a bit thicker (and therefore smaller) internally to handle the increased pressure. The case capacity of the 5.56 is 28.5 grains of water, while the .223 carries 28.8. That may not seem like a huge difference, but the important thing to remember is the 10,000 psi difference and how that might affect your guns.

Don’t Gamble: Always Use The Correct Round

Here’s where the rubber meets the road with these two rounds: Do not fire 5.56 rounds in guns chambered for .223 Remington. Period. End of story.

You might think, “Well okay, but my buddy Bubba does it all the time and he’s still alive.” Little did you know, Bubba has a gambling problem, because that’s exactly what it’s like shooting 5.56 through a gun chambered for .223: gambling. Just like gambling, the house always wins. Repeatedly exposing a .223 chamber to 5.56 pressures causes metal to weaken over time, which eventually will lead to a rupture that can have dire consequences.

Unique Qualities of 5.56 Cases

Unlike .223, some 5.56 cases have a crimped primer, which makes decapping (popping the primer out) more difficult during the reloading process. Some primers also have a colored (red, blue, sometimes purple) waterproofing sealant.

You might also notice some annealing around the shoulder, which appears as a slight discoloration. Annealing is a good thing — it’s a heat treatment that restores the brass’ original malleability lost during the original loading process. Annealing lets the brass expand and contract when fired, which aids reliability. Annealing can be seen on the shoulder of this M193.

What Guns Shoot .223/5.56?

Most 5.56 guns are semi-automatics, like the AR-15. There are some target ARs that are chambered for .223, but not many. The pressure difference is the reason. If you're in the market for an AR, make sure you get one chambered in 5.56 (you can tell by the roll mark/stamp on the barrel). If you get a 5.56 barrel, you never have to worry about the gun exploding and you can also shoot .223 as well.

If you’re looking to get a hunting rifle or a bolt-action, most are chambered in .223. This makes sense because the .223 is more of a sporting round with a wider variety of bullet types. Again, make sure to avoid using 5.56 in these guns. All dangers aside, it won’t be as accurate as .223 because twist rates good for heavy hunting bullets aren’t so good for lighter 55-grain pills.

.223 vs. 5.56 Performance and Ballistics

These rounds are close enough that their performance is pretty similar, but the difference lies in the bullets themselves (the projectiles that actually fire).

A lot of military-style M193 5.56 is loaded with a 55-grain FMJ bullet that may or may not have a boattail. Military accuracy standard for M193 from a service rifle is roughly 4 MOA (Minute of Angle) at 100 yards, which is about a 4” group at 100. That’s not going to win any marksmanship contests, but as the saying goes, when a manufacturer is cranking out billions upon billions of rounds, it’s close enough for government work.

True M193 is a spicy little round that sends the 55-grain bullet zipping along at 3,150 fps or so. That’s good enough to keep it supersonic (greater than +/- 1,200 fps) at 500 yards, which was one of the military’s initial requirements. We say “true M193” because the vast majority of stuff labeled as such isn’t as fast as real M193, which means it won’t deliver the same terminal performance as the real deal.

When an M193 5.56 impacts a soft target, it’s designed to turn 90 degrees and split apart, making for a savage wound channel. However, if you're running a short barrel (say 10.3” or so) you probably won’t see this kind of performance because the shorter barrel decreases velocity. WIth a short barrel, you’re better off with a different bullet that is less velocity-dependent for its lethality (such as a soft point or one with a polymer tip that initiates expansion).

Regarding ballistics, .223 and 5.56 are nearly identical. There's no real need to separate the two. But, to see better performance out of these two, barrel length matters. You’ll choose your barrel length based on what you’re using the gun for. Hunting? Think 16” to 20” or more with a 62-grain .223 bullet or heavier. Home defense? You’ll want a shorter barrel and a good, reliable 5.56 or .223 load. Plinking? Try a bulk pack of .223 or 5.56. There’s really no need to parse it out any more than that.

Best .223/5.56 Ammo

The .223 and 5.56 are the most popular centerfire cartridges in America because of their versatility, affordability, and minimal recoil.

5.56 for Hunting and Shooting

Its diehard fans love the 5.56 because it’s a lightweight, flat, and easy-shooting round. With the AR-15 using standard capacity 30-round magazines, it offers a good degree of firepower. Critics of the round say it lacks the “knockdown power” of the 7.62 and that terminal performance is poor past 200 yards, neither of which is totally incorrect.

Despite these claims, the M193 and most other 5.56 rounds are exceedingly reliable. That should be priority No. 1 for any hunter or shooter, and just about all flavors of 5.56 will do the job. That’s why bulk pack 5.56 is great training and plinking ammo.

The Versatility of .223

The .223 isn’t mass produced on the scale of the 5.56, and manufacturers generally keep a pretty tight check on consumer goods. There are a wealth of bullets that are loaded into .223 ammo, from blistering 30-grain varmint zappers to 77-grain precision pills. This makes the .223 a versatile performer from prairie dog towns to the deer woods.

A 62-grain bonded soft point or a 77-grain Razorcore provide strong medicine in a home defense carbine while also working on deer-sized game (where legal). Speaking of legalities, while some states do permit .223 for use on deer and the like, none permit the use of FMJ rounds (like the M193) for game. Anything goes when you’re shooting predators or invasives like hogs, but for game species, you need a round that expands (hollow point) or deforms (soft point) because they’re more reliably lethal than FMJ bullets.

Which One Is Cheaper?

When it comes to training and plinking, .223 usually gets the nod because certain flavors are cheaper than 5.56. Steel-cased .223 is the cheapest thing you can feed your AR or .223/5.56 gun. That said, you get what you pay for. You don’t have to look long on the Internet to come across volumes of horror stories regarding steel-cased ammunition and the headaches it causes. The fact of the matter is, most of the uber-cheap stuff that was seriously problematic is no longer made in the U.S. but is imported from elsewhere. The vast majority of today’s steel-cased ammo is polymer coated. While it’s certainly dirty to handle and fire (and increases wear and tear on your gun’s internal parts to some degree), it won’t jam your gun like lacquer-coated ammo will.

Reloading .223/5.56

Another downside of steel-cased ammo is that it’s tough to reload. Steel doesn’t have the ductility that brass does, and gets brittle after firing. Trying to resize a steel case is usually a waste of time. Don’t be cheap — pony up for the good stuff if you plan on reloading, and you’ll be ahead by the second time you fire it. What would your friends think of you if they knew you were picking up steel cases?

When it comes to reloading, many shooters pick up .223 and 5.56 brass and throw ‘em in the same bucket. However, if you give a .223 case and a 5.56 case the same shot of powder, you’ll see a greater velocity standard deviation (a huge factor in accuracy) than you would if you used just one kind of case. This is because the thicker 5.56 brass reduces the case capacity by a hair, and dumping equal amounts of powder into a .223 case and 5.56 case will yield higher pressure in the 5.56.

If you’re just reloading to make noise at the range, Godspeed and fire at will. However, if you’re wanting to make precision rounds, don’t just use either .223 or 5.56. Use the same brand of .223 brass or 5.56 brass with the same year and manufacturer. Tiny differences like these will shrink your groups on the bench.

The Bottom Line: Which is Better?

The .223 Remington and 5.56 NATO are opposite sides of the same coin. With a shared lineage born of a project to create a lightweight, high speed cartridge, these rounds perform a wide variety of tasks very well. Whether you’re punching holes in paper, critters, or bad guys, the .223/5.56 are both admirably suited for the task.

However, the question of ‘which one is best’ invariably comes up in these conversations. You already know the answer: it depends. If you’re going to be shooting from a bench or at critters, go with .223 over the 5.56 ammo. A .223 bolt-action gun will be more accurate. If you’re looking for a home-defense gun, go for a 5.56 AR. It gives you a greater degree of versatility and the utmost in reliability.

Either way, when used in appropriate applications, the .223 and 5.56 are fantastic cartridges capable of delivering a lot of performance for a little dough. At Pro Armory, we've got plenty in stock of both .223 Remington and 5.56x45mm NATO cartridges — all available for the lowest shipping prices possible.

Need help choosing the right round? Give us a call! Our team of veterans and ammo enthusiasts is ready to help you choose the perfect round for your needs.