.223 Remington vs 5.56 NATO

What is the difference? Which one should I use? 

New AR-15 owners may be looking at boxes of ammo wondering which is better for their rifle; 223 Rem or 5.56x45mm? In the ammo industry, we use a lot of jargon and shorten words out of bad habit. For example, 223 Remington is the same as 223 Rem, it’s simply short hand.

The same thing is true for 5.56x45mm, it is the same as 556 Nato, or can be abbreviated as 5.56 or 556. Ultimately, you want to make sure you check the markings on your barrel as all barrels show the caliber the barrel is chambered in. A 556 barrel can shoot 223 Remington, but a 223 Remington barrel cannot shoot 5.56 ammo. Where things can get confusing, is when a barrel is chambered in 223 Wylde. These barrels can shoot 556 ammo and 223 ammo. The Wylde terminology has nothing to do with Remington.

Most firearm owners have probably wondered to themselves at some point: “What is the difference between 223 Remington and 5.56x45mm NATO?”. The difference is actually quite simple. Based on who you ask and where you look, you’ll find a lot of different answers that can get confusing.

Some might say that the only difference is the box it comes in, while others might say that the differences between the two can determine whether you spend your range day shooting or at the hospital with a broken rifle. So, what is truth and what is folklore?

What does Green Tip Mean?

To further complicate matters between 223 and 556 ammo, 556 will usually have the specification on the box of M193, SS109, or M855 which means it is green tip. Green tip ammunition contains a steel core wrapped in lead and a full metal jacket projectile.

You DO NOT want to shoot green tips at indoor ranges because it can cause sparks and potentially a fire or at steel targets due to splatter and the ability to ruin or pit the steel targets. M855 ammo is light armor piercing. The green tip on M855 is so that you can easily identify the projectile.

M193 spec ammo can also be referred to as ball ammunition, this is great target practice ammo that can be shot at steel or indoors. The projectile is all lead with a full metal jacket and does not contain steel in the projectile.

SS109 5.56x45mm ammunition is the same as M855 spec ammo in that the projectile features a steel core with lead around it wrapped in a full metal jacket. The only difference is that SS109 typically won’t have a green painted tip. This spec ammo should not be shot at indoor ranges or at steel targets.

If you’re not sure if you have SS109 or M193, simply grab a magnet and put it to the projectile. If it sticks, you have SS109 or M855, if it doesn’t attract to the magnet, you have M193 spec 5.56 ammo.

Where did .223 and 5.56 Come From? 

To give some context, the 223 Remington round was the United States’ response to the proliferation of the 7.62×39 cartridge. This cartridge was an in-between round that allowed fighters to carry more ammo into battle while keeping the weight low.

The 223 Remington round began development in 1957. It was based off of the 223 Remington round, but with an elongated case and shortened neck. This allowed for a larger powder charge. This led to a new cartridge. It outperformed the old 223 Remington substantially. It was adopted by the military only a year after it was released to the civilian market.

The cartridge was comprised of a 55 grain full metal jacket round that carried 1294-foot pounds of energy at 3260 feet per second at the muzzle. This new, faster, and lighter spec round was designated and standardized as 5.56 x 45 M193, which eventually became the round that we all know and (most) love today.

So… What is the Difference?

In terms of external dimensions, the cartridge cases themselves are identical between 223 Remington and 5.56x45mm NATO. One of the main differences between the two rounds can be found in chamber dimensions. 5.56 NATO chambers typically have a 0.162″ lead, while 223 Remington is usually 0.085″. Having a longer leade can help increase reliability and prevent carbon buildup and other debris from jamming the action. This has the added bonus of higher muzzle velocities, but it comes at the very slight expense for the accuracy.

Differences can vary dramatically and are often dependent on different manufacturer loads and projectile weights. For example, a very popular 223 Remington round that we carry (PMC Bronze 223 55gr FMJ) has a muzzle velocity of 3200 feet per second. Meanwhile, the 5.56 equivalent (PMC X-TAC 5.56 NATO 55gr FMJ) has a muzzle velocity of 3270 feet per second.

Another difference, from which many misconceptions and confusion stems from, is the increased chamber pressure that 5.56 NATO reaches. 5.56 NATO chamber pressures can often reach up to 60,000psi, while the average chamber pressure of a 223 Remington load is around 55,000psi. Other difference examples down below:

What is 223 Wylde?

The great debate between the 223 and 5.56 round has been shared and examined over a million times. However, a new type of round has put more questions into the minds of AR-15 rifle owners: the 223 Wylde. The 223 Wylde round is a hybrid rifle chamber. It allows you to shoot both 223 and 5.56 from the firearm safely.

A 223 Wylde rifle has an identical chamber angle as a 5.56 AR-15 rifle but also brings a .2240 “Freeborn diameter” refers to the tighter freeborn size in a 223 Wylde rifle. This allows you to shoot 223 ammo with strong accuracy, which is arguably more accurate than 5.56 ammo.

What Round Should I Use?

As a result of these pressure differences, 223 Remington is perfectly safe to shoot in both 5.56 and 223 chambers. 5.56 ammo is only safe to shoot in rifles that are chambered for 5.56. For the majority of us, modern AR-15 rifles are being used. This is typically a non-issue that will not affect the safety of that firearm. Most chamberings made today use 5.56 NATO specifications.

Older firearms may be more likely to have 223 Remington chamberings. Therefore, it is especially important to verify before use. Just like with anything else involving firearms, you should always err on the side of caution. Make sure that the rifle you are using is chambered for 5.56 NATO before using 5.56 ammunition.

If you’re looking to order any of the 223 bulk ammo, 5.56 bulk ammo, or these calibers by the box please visit our website at trueshotammo.com, call us at (888) 736-6587 or, you can email us at [email protected].