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One question we see oftentimes with new AR-15 owners is about caliber options. .223 Remington or 5.56 - which should they choose? The cartridges are fairly similar overall, but they are not 100% interchangeable. We think the answer is an easy one but that doesn’t mean there is only one side to the coin. Let’s take a deeper look at 5.56mm and .223 so we can make the best decision for our needs. Read on!

.223 Remington

In 1958 Remington Arms released the .223 Remington and began work with ArmaLite to work on a cartridge for the U.S. Army for use in a carbine. Based on the first modern rimless centerfire cartridge, the .222 Remington, the .223 changed casing size down to a 45mm length. In 1962 in conjunction with the U.S. It became widely available for civilian use and was also being used in the M16 for the U.S. Army. The first widely available rifle for the civilian market was the Colt AR-15. .223 Remington is still to this day one of the most widely used calibers in America.

Ballistic Performance

Ballistic performance is largely dependent on the bullet mass, as well as velocity and cartridge load. .223 Ballistics as such can vary widely depending on what the shooter chooses to run in their gun. Some various bullets include:

• 36-grain Jacketed Hollowpoint: Has a speed of 1140 m/s.
• 55-grain Nosler ballistic tip: Has a velocity of 990m/s.
• 69-grain BTHP: Has a speed of 900m/s.

5.56mmx45mm NATO

As we know, NATO has developed standardized loads for member countries. This allows for standardized specifications for each member country making their own ammo. When it comes to 5.56, NATO developed this round from the .223 Remington in the early 1970s. The Belgian company FN Herstal began to change the .223 into a round for a light machine gun and from that was born 5.56x45mm. The new 5.56 utilized a 62 grain bullet that was made to penetrate helmets out to 600 meters.

When ArmaLite sold the AR-15 design to Colt in 1960, Colt immediately began to improve the weapon. They moved heavily for a U.S. Government contract knowing the military’s need to replace the aging M-1 Garand. The rifle eventually was adopted and began seeing serious duty-use in the Vietnam War. Today the 5.56mm is not only still in use in the U.S. Military but many other NATO countries. If it ain’t broke don’t fix it as they say.

Ballistic Performance

As stated above - ballistic performance is largely dependent on the bullet mass, as well as velocity and load. 5.56 loads will also vary widely depending on the cartridge, but here are a few examples:

• 4.0g(62-grain) SS109 has a velocity of 948m/s.
• 4.0g(62-grain) M855A1 has a velocity of 961m/s.
• 4.1g(63-grain) GP90 has a velocity of 851 m/s.

5.56 Armor Penetration

Remember when we said earlier that the 5.56mm NATO was designed to pierce helmets out to 600 meters? We weren’t joking. The US Military 5.56mm round - called the M855 can indeed penetrate 3mm of steel at 600 meters and 12mm of steel at 100 meters! This means the 5.56mm is a formidable opponent to body armor.

Because of this, Level IV armor plates must be used with a steel core plate to safely defend against 5.56mm. Most professionals wear Level IV armor and civilians can also buy Level IV armor plates.

5.56mmx45mm NATO vs .223 Remington

5.56 and .223 Remington dimensions are essentially identical, so why can’t you shoot 5.56mm in a .223 Remington weapon? Actually, the shoulder and neck width and the 5.56 has thicker walls to the cartridge for higher chamber pressures.

For this reason we must NEVER shoot 5.56mm in a .223 Remington chambered weapon. You CAN shoot .223 Remington in a 5.56mm gun, however.

The .223 Remington chamber create a tighter seal on the cartridge and because of this creates more pressure. Leade is a term describing the distance between the case mouth and where the rifling begins in the barrel. The length and diameter of the leade is called the freebore. The freebore for a 5.56mm is wider and longer which means a longer free space the bullet will travel before hitting the barrel rifling. It’s all about the pressure building in the chamber between the two rounds.

So which one should we choose? To us the answer is simple. Buy a 5.56mm gun and you can shoot both! Most AR-15s are labeled “Multi-Cal” for this reason, meaning we’ll be able to shoot 5.56mm and .223 in the same gun! (You can also shoot .22LR or .223 Wylde)

Both calibers even fit the same magazines so this is really a nonissue. If you see a barrel with .223 Wylde on it that will also mean you are good to safely shoot both calibers. 

5.56mmx45mm NATO vs .223 Remington Price

So what about price? Ammo shortages have caused both .223 Remington and 5.56mm NATO to jump in price - same as all ammo. Nonetheless both rounds still may be found reasonably priced at the time of this writing. Winchester 55 grain FMJ in 5.56 may still be found in the $.60/rd price range and other 5.56mm rounds can be had in the $.77/rd range. Obviously, hotter and specialty loads will be more expensive.

.223 Remington is found on average in the $.50/rd- $.60/rd range on average for FMJ in the 55 - grain range up into the $1.00-$1.50/rd range for specialty rounds. Because the 5.56mm rounds are usually a bit hotter loaded it makes sense that they will be a bit pricier.

Start your next build with Modulus Arms

Hopefully this helped answer the questions over .223 Remington vs. 5.56mm. At the end of the day both cartridges are so similar that it almost makes no sense to purchase a rifle with a barrel specific to .223 Remington if the 5.56mm is available in the same platform. Grab an 80 lower from us today and you can start on your next AR15 build and shoot both calibers! Just make sure your barrel is chambered for 5.56 NATO or .223 Wylde.