5.56 vs .223: What Is the Difference?

What is the difference between 5.56 and .223?

The two cartridges share nearly the same outside dimensions, but 5.56x45mm NATO is loaded to higher pressure and its chamber has a longer leade. A rifle chambered in 5.56 NATO can safely fire both .223 Remington and 5.56 ammo. A rifle chambered only in .223 Remington should be fed .223 unless the manufacturer says 5.56 is approved, because the higher pressure can be unsafe. Always check the chamber marking on your barrel and your owner manual. When in doubt, match the ammunition to the exact marking stamped on your barrel, and ask a gunsmith if the marking is worn or unclear. Many AR-15 style rifles are marked 5.56 NATO, while many bolt-action and older rifles are marked .223 Remington.

Browse 5.56 NATO and .223 Remington side by side.