While similar, when comparing the 5.56 versus .223 these two rounds are more like cousins than identical twins.

Since its adaptation as the standard issue military round, the 5.56 NATO has risen in popularity to near meteoric levels. Likewise the .223 Remington is one of the most popular rounds among sportsmen. Year over year the combination of 5.56/.223 dominates rifle ammunition sales. While the two rounds are very similar in looks and performance, there are some very minor, yet very important differences, as we look at the 5.56 vs .223.

History On 5.56 Versus .223

In the olden days the U.S. military preferred heavier, slower rounds for military conflict. After World War II however, armed forces desired a standard-issue firearm that would support higher capacity magazines. This led to the development of the M14, a 7.62 caliber rifle sporting a 20-round magazine. While the M14 solved some of the deficiencies of the M1 Garand, it still lacked in functionality.

When fired at full-auto, the M14 produced significant heat and muzzle rise that made the gun relatively inaccurate. Furthermore the 18” barrel and nine-pound total weight reduced handiness in dense cover and urban environments. Once again the military sought a round and pairing firearm bent toward the positive aspects of the M14 and corrected its inefficiencies.

The .223 was developed as a fast, flat-shooting cartridge that would be more efficient and more accurate in fully automatic, shoulder-fired rifles. Later it was modified to hold a heavier bullet that produced more downrange punch. The round was adopted as the standard-use cartridge by NATO in 1980, and the 5.56 NATO was born.

Differences in Construction

The biggest difference in the construction of 5.56 versus .223 is the amount of pressure produced when firing. In standard production rounds, 5.56 NATO ammunition is packed with slightly more powder, creating a slightly faster round. 5.56 ammo also utilizes a heavier bullet than most off-the-shelf .223 ammunition. That combination of more powder and heavier bullets creates more pressure in a rifle’s chamber.

5.56 chambers are specially made for the added pressure, specifically by increasing the length of the leade in the chamber. The leade is the distance from the bullet’s resting place in the chamber to the point where the bullet makes contact with the rifling in the barrel. That added space neutralizes higher pressures, which are then blown out rather than directed back into the casing.

The shorter leade in a .223-specific chamber retains more pressure and ensures a tighter seal between the bullet and the chamber. With the tighter seal and more pressure retained inside the chamber, the pressure must be reduced to prevent over-pressurizing the chamber and damaging the rifle.

Operation and Performance Differences

While the two cartridges are modifications of the same platform, they aren’t always interchangeable. A .223 round is compatible with a 5.56 rifle in most cases. On the other hand, a 5.56 can significantly damage a barrel and chamber when fired from a rifle only designed to shoot .223. Not to mention potentially harm a shooter’s face and eyes. The .223 barrels are simply not built to withstand the same amount of combustion when put under stress. Both rounds tend to fit the same magazines however and can usually be chambered in the same rifle regardless of cartridge specifics. Shooters must be certain to match their ammunition to the appropriate rifle.

5.56 Versus .223

When comparing 5.56 vs. .223, the two rounds also produce slightly different results downrange. The heavier bullets of the 5.56 are more capable of bucking wind and providing consistency in harsh conditions. On the other hand, the .223’s tighter seating in the chamber means the round doesn’t have to travel as far to engage a barrel’s rifling. That quicker contact provides quicker stabilization of the round and more accuracy at longer ranges.

The 5.56 was initially intended to be shot from a select-fire semi auto/auto combat rifle and to have an effective range of 500 yards. When shooting further distances, the .223 is considered the more accurate of the two. Most .223-specific rifles are built on a bolt action chassis.

While very similar and branching from the same family tree, the two are more like cousins than identical twins. Originally the .223 was built as a lighter, more precise round while the 5.56 was envisioned as its beefier upgrade. Both are fantastic rounds that consistently confirm their popularity with ammunition sales. While shooters must use caution when intermixing the two, they both provide a world of opportunity at the range and in the field.