The 5.56 mm round, AKA the .223 Remington, is a popgun caliber.  Useless past 300 or 400 yards, because the bullet derives it's killing power from velocity and velocity drops off with increased range, particularly in short-barreled weapons such as the M4.  It's a 50 year old obsolete jungle warfare caliber better suited to shooting ground hogs than people.  You may have heard the stories about its uselessness that have been emanating from the sandbox for years.

So what do we do?  Millions of Americans are hoarding 5.56, as if it makes any difference.  It won't penetrate a threat level III armored vest past 300 yards.  Yeah, it will trash one of those cool-looking Kevlar helmets all the tough guys like to wear for the photographers, and splatter their brains, but who can do a head shot at 300 meters with an AR 15 or equivalent?  Only a few of us.

The thing the scumbags should worry about are the lone riflemen with .308's, 30-06's, 7mm Magnums, 6.5x55's, .270's, .338's and .375's.  They'll trash a trauma plate at 500 yards, and all that cool looking body armor is just extra weight you have to hump and slows you down.  And there are millions of us out here with those calibers, and we can shoot.

So don't get too cocky, assholes.  It won't all be urban warfare.  Take a walk in the woods...