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
5.56 NATO vs 223 Rem vs 223 Wylde: Pros, Cons, And Dangers
223 vs. .308 Caliber Comparison
223 Rem vs 5.56 NATO
223 vs 5.56: The Ultimate Comparison & Review
22LR vs 223 (5.56mm) what's the difference?
223 Remington vs. 5.56 NATO - What's the Difference? – Top Brass Reloading Supplies
223 vs. 5.56 - What's the Difference? - The Broad Side
223 vs 5.56: Comprehensive Caliber Comparison by
5.56 vs .223: What Shooters Need to Know
5.56 NATO vs. .223 Remington: What Is the Practical Difference?
223 vs 556: What's the Difference?
5.56 vs 223 Ammo - What's the Difference? 19 Things You Need To Know
556 NATO vs 223 REM what's the difference? How to identify chamber size - Part 2
5.56 vs 223 Ammo - What's the Difference? 19 Things You Need To Know
223 Rem. Vs. 5.56x45mm