What is the real difference between .223 and the 5.56 designation

[jonbearman]

I have a friend at work who is worried about shooting m193 ball ammo(lc89) to be exact in his bushmaster.The reciever is stamped .223 and the barrel is stamped 5.56.What is the scoop?

 

[coyoteklr]

one is inches and the other is mm.... most of the military ammo will work in just about all ar's some of the old...old...old military would only shoot one or the other .... i have two bushy's but the lowers are stamped .223 and 5.56....
never saw a bushy with any age that wouldn't shoot both.......but i suppose to be on the safe side and quick phone call would settle it .......
i'm assuming he got a boat load for pennies on the dollar and wants to pray and spray... that is 22years old,hate to see him try to blow a squib out with another ball.... but have seen some guy's shoot really old 06 stuff and it worked.....most of the time the two numbers are verbally interchanged....
rock river has a wilde chamber that will shoot both.... supposedly......

 

[Cheechako]

The only difference in the chamber, if any, would be in the throat. And possibly the twist may not be correct for the bullet weight.

Ray

 

[Killshot]

As mentioned, it's a chamber/throat issue. If the barrel is marked 5.56 he can safely shoot both 5.56 and .223. What the lower receiver says is unimportant.