&quot;Do you know why the current calibre for most nato guns is 5.56mm? yes partly because its smaller, partly because there is less kick, but also because its less lethal.&quot;<p>This is actually a myth - the .223 was not selected because it&#x27;s designed to injure instead of kill. The main advantage of the round is that it&#x27;s light, so soldiers can carry a lot of ammunition on them, but it also has a flat trajectory and is quite lethal within typical combat ranges. You also get the advantage that it&#x27;s easier to shoot a .223 quickly than a larger caliber - a soldier can put 30 rounds down range with more accuracy, in less time, than they can with a larger caliber.