5.56 vs .223: What's the Actual Difference?

Summary

This article clarifies the common confusion between 5.56 NATO and .223 Remington ammunition, explaining that while the cartridges appear identical (both using a .224-inch bullet diameter), the critical difference lies in the chamber design, specifically the leade (throat) length. It advises that barrels marked 5.56 NATO or .223 Wylde can safely fire both ammo types, but barrels marked .223 Remington should only use .223 ammo due to potential overpressure issues.