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What Caliber is .223 Equal To?


When it comes to firearms and ammunition, understanding the equivalency between different calibers is crucial for gun enthusiasts and shooters alike. In this article, we’ll answer the question “What caliber is .223 equal to?” and explore into the similarities and differences between the .223 and 5.56mm cartridges, considering their interchangeability, physical dimensions, and the implications for firearm usage.

Exploring the Similarities

Size Comparison

The .223 Remington cartridge and the 5.56x45mm NATO cartridge share nearly identical physical dimensions. Both cartridges feature a bullet diameter of .224 inches, making them practically equal in size. This similarity allows for interchangeability between firearms chambered for either cartridge, with .223 ammunition typically compatible with 5.56mm chambers and vice versa.

Interchangeability in Firearms

Due to their similar dimensions, firearms designed for .223 Remington cartridges can often safely chamber and fire 5.56x45mm NATO ammunition. Similarly, rifles chambered for 5.56mm NATO can typically accommodate .223 Remington cartridges without issue. This interchangeability adds versatility for shooters, allowing them to use either cartridge based on availability and preference.

Understanding the Differences

Pressure Variation

While .223 and 5.56mm cartridges share external dimensions, the most significant difference lies in their chamber pressures. 5.56x45mm NATO ammunition is loaded to higher pressure levels compared to .223 Remington cartridges. This higher pressure is necessary to meet military specifications and ensures optimal performance in combat scenarios.

Implications for Firearm Usage

The variance in chamber pressure has important implications for firearm safety and performance. Firing 5.56mm NATO ammunition in a firearm chambered for .223 Remington can lead to increased chamber pressure and bolt thrust, potentially compromising the integrity of the firearm and posing safety risks. Therefore, shooters should always consult their firearm’s manual and adhere to manufacturer recommendations regarding ammunition compatibility.


The .223 Remington and 5.56x45mm NATO cartridges are nearly identical in size, allowing for interchangeability in many firearms. However, shooters must be aware of the differences in chamber pressure between the two cartridges and exercise caution when using them interchangeably. By understanding the equivalency and differences between these popular calibers, shooters can make informed decisions and ensure safe and effective firearm usage.

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