The .223 and 5.56×45 NATO cartridges are nearly identical rounds that have led shooters toward countless debates, confusion, and frustration. But understanding the differences between these two rounds isn’t all that difficult when you cut you through the misinformation. In fact, with just a little background information about each cartridge and an understanding of how you plan to use your firearm, you’ll find yourself better prepared to make a decision between the two calibers. You’ll also know the risks, if any, of shooting a 5.56 round in a .223 chamber.
The History of .223 & 5.56
Remington submitted the .223 Remington round to SAAMI(Sporting Arms and Ammunition Manufacturers Institute) in 1962 as a sporting round generally considered a varmint cartridge. Since then, .223 Rem ammunition really hasn’t changed in terms of cartridge dimensions or the pressure that it is loaded to, according to Gun Digest 2013. That makes sense, as SAAMI is pretty rigid with their testing and once a standard is set, it tends to remain that way for the life of a given caliber. While variances on the .223 Remington round have popped up, such as the .223 Wylde, which is a round many feel is a good compromise between the pressures and performance of .223 and 5.56, .223 Remington is far and away the most popular of the .223 calibers.
On the other hand, 5.56×45 NATO has never been submitted to SAAMI because it’s a military round, loaded to a military standard that is quite different from SAAMI’s standards. As you can imagine, military standards are very exact and quite rigid all over the world. That’s not to say military standards are better than SAAMI, it’s simply that the way they each measure different attributes of a round are different so you can’t truly stack the rounds side-by-side and understand the differences between them. This variance in standards plays a huge role in the confusion that surrounds the .223 vs. 5.56 debate today.
In summary, the military measures pressure one way and SAAMI measures pressure in a different manner so the two calculations can’t be compared side-by-side, helping spur more discussion, confusion, and even misinformation about these two calibers.
Are 5.56 and .223 Rounds Interchangeable?
In terms of the exterior dimensions, 5.56×45 and .223 cartridges are just about identical so there are not really any concerns about fitting each round in your chamber, it doesn’t matter if you’re chambered for .223 or 5.56, the round will likely load. However, pressure varies between the two rounds and that pressure change can be significant depending upon your firearm. Generally, 5.56×45 ammunition fires at a higher pressure than .223 Remington ammunition. A typical range round of 5.56×45 will hit a peak pressure of around 60,000 pounds per square inch while a comparable .223 cartridge’s peak pressure will be about 20-percent less.
To help function under those increased pressures, many 5.56 chambers are larger in critical areas than .223 chambers. Specifically, the area of the chamber known as the leade or throat of the barrel will be different. This throat or leade portion is the area of the barrel in front of the chamber just before the rifling begins. So, if you load the same exact round in both a .223 chambered firearm and a 5.56 firearm, the extra area in the 5.56 chamber will help safely handle the pressure loaded cartridge and potentially lead to less potential wear and tear than if you fired the 5.56 NATO round in a .223 Rem firearm.
Also of note, odds are you’re going to get slightly faster muzzle velocities using 5.56×45 ammunition than you would if firing .223 Remington.
So what does it mean? For most shooters, the general rule of thumb as it relates to each round is that you should not fire 5.56 in a firearm chambered for .223 while you can safely fire .223 in a 5.56-chambered firearm. But it’s not that cut and dried.
There are several cases where shooters have documented firing 5.56 in their .223 firearms with no major problems and while a major malfunction, such as an explosion is possible, it is extremely unlikely to happen. You see part of what led to this way of thinking is because of the SAAMI standards for testing. Given a highly pressurized barrel, 5.56 rounds in a .223-chambered firearm are not a great idea. Most civilian .223 rifles on the market today, however, are much more forgiving than the barrels used for SAAMI standard testing so you’re likely to not only avoid major malfunctions but you’ll likely not even be able to tell the difference when firing 5.56 in a .223 Remington chambered AR-15.
Keeping that in mind, if you are relying on an AR-15 in a survival situation, you will likely want to invest in ammunition that is ideally suited for your specific chamber. Because of the pressure each round is loaded and the tolerances accepted by most modern sporting rifle barrels, even if not ideal in terms of wear-and-tear, you will likely be able to effectively neutralize a target using either caliber.
How to Tell .223 Remington and 5.56×45 Cartridges Apart
So you’re stuck in a place where ammo is scare and you come across rounds that appear to be appropriate for your firearm. Since .223 and 5.56 are nearly identical in physical appearance, how do you know if it’s .223 Remington or 5.56×45 ammo? The quickest and easiest way is to examine the head of the cartridge. If it’s 5.56, it’ll be stamped be stamped with a NATO insignia, which looks like a circle with a plus sign (+) inside of it. If it’s .223 Remington, it’ll say .223 Rem.
Photo Credit: TheFiringLine.com
So Which Caliber AR-15 is Better?
The short answer about which caliber is best for you depends on your particular needs. The .223 Remington is the mostly widely produced caliber and while you likely won’t want to fire 5.56 in your firearm often, in an emergency you could easily get away with firing a few hundred rounds if necessary. The bottom line is this: if you want to be as safe as possible, always shoot .223 Remington ammunition. The .223 Rem cartridges will safely fit and fire in any rifle chambered for either .223 or 5.56.
In terms of pricing, .223 ammunition and 5.56 ammo cost about the same amount per round and both are readily available most of the time on the U.S. civilian market. If you’re not sure what you’ll be using the firearm for, most shooters find 5.56 chambered firearms more appealing because of the flexibility they offer when it comes to firing either .223 or 5.56×45 rounds.
About the Author:
Mark Ollendale is a life-long shooter and firearms enthusiast obsessed with ammunition. Passionate about helping protect the 2nd Amendment while spreading the benefits of firearm ownership to new shooters young and old, Mark works for online ammo retailer AmmoForSale.com.