223 Remington vs. 5.56 NATO - What's the Difference? – Top Brass

Case cartridges for the 5.56 NATO (5.56 x 45 mm) and the .223 Remington are very similar. For all practical purposes, the external dimensions are identical, and one can effectively say that there exists no difference between the two. Both are designed to accommodate a .224 inch (5.56 mm) bullet between 40 to 85 grains

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