at the gun show today, i noticed that some of the ar's had 223 on the side of the receiver and some had 5.56 and then others had 5.56 nato. are all the ones marked 5.56 made for the nato round or what? was going to pick up a lower , but got a lttle confused about this. thankshinking.gif

The stamping on the lower have little to do with the situation.
The chamber is cut into the barrel,different manufacturers have different spec on their chambers and there are no hard and fast standards. The difference between a 5.56 chamber and a .223 are not huge to begin with and there are aparently some gray areas. I am not claiming it doesn't matter. There was a post several weeks back-search on headspace gages. The post discused some of the dimension differences
and which companys were claiming to use what.
The lowers are all interchangeable,talk to whoever makes the barrel you are going to buy about what the chamber is.

Lowers will make no difference when it comes to .223 or 5.56 barrel

The difference comes when you try and shoot 5.56mm ammo in a .223 chambered barrel.

Most likely, it wont have any problems.  But there is that one thats going to blow your mag apart and ruin your lower.

EDIT:  Right Grizzlyarms?

the lower itself has no rear control over 5.56 or .223

here is some reading on the chamber.
www.ammo-oracle.com/