If you’re like most gun owners, odds are you’ve already got an AR-15 chambered to shoot either .223 Remington or 5.56x45mm NATO.

If you don’t already have an AR or MSR in one of these two cartridges, you might be asking, “which cartridge is best?” Read on to learn the basics of each cartridge and how 223 and 556 compare.

223 vs 556 Basics

223 and 556 ammunition is among the most available and cost-effective ammo options, used for target shooting, competition, personal defense, varmint, or even small game hunting. You’ll find all kinds of semi-auto rifles, bolt-action rifles, carbines, and even pistols chambered in both rounds.

While not interchangeable, 223 and 556 share common DNA. Both cartridges were designed for military use. In lightweight service rifles, these small-caliber, high-velocity rounds facilitate rapid fire and performance on target.

Cartridge History

Developed in the late 1950s, 223 Remington was pioneered for the US Army’s iconic M16 rifle. 223 quickly became the go-to ammo for the everyman rifle. Generations of American service members have shot 223, with the round still in use decades later.

Technology marches on. In 1970, NATO members saw the need for a smaller cartridge to complement the larger and heavier recoiling 7.62x51mm. Working with a European arms manufacturer, the fine folks at NATO decided to Frankenstein the 223 Remington to make it bigger faster and stronger. And so, the 556 was born.

What’s the Difference Between 223 and 556?

So, what’s the difference? 556 rounds are higher pressure, utilizing different powder, slightly more powder and (usually) heavier bullet weights. To accommodate the bigger and heavier bullets, 556 rifle chambers are larger, using a longer throat. Correspondingly, 556 barrel twist rates are faster than their 223 cousins. This better stabilizes the 556’s bullets in flight.

Can you shoot 556 in a 223 Rifle? 223 in a 556?

You can safely shoot 223 Remington ammunition in a rifle chambered for 556. Due to the increased pressure of the 556 round, NEVER shoot 556 ammunition in a rifle intended for 223. Always read your user manual.

Choosing a Cartridge

As always, your cartridge pick should depend on your intended use for the firearm. Picking an AR cartridge for varmint hunting vs choosing a cartridge for home defense or long-range competitive shooting leads you to different answers.

556’s heavier bullet grain weights might perform more consistently afield in shorter carbine barrels. Because of the round’s higher pressure and increased powder weight, 556 can maintain terminal velocity at further ranges. As the round is still used by the US military, you can find surplus milspec ammo in 556 as well.

223 is also eagle-eye accurate at long distances and remains the choice of many long-range competitors and shooters. More bolt action rifles are chambered and available for 223 vs 556, so if you want a bolt action for prairie dog hunting or bench rest shooting, 223 could be your choice. 223 ammo is also generally cheaper than 556.

Apples to apples, 223 and 556 perform similarly in most platforms, so there’s no wrong answer. The best way to pick? Head to the range and test out both.