HI guys!!   i'm new to this rifle and i'm getting ready to order my first lower. now i'm scratching my head!!  whats the diff  between 5.56nato  and the  .223  marked lowers?? i've seen them marked both ways. what i'm trying to do is to set a rifle up with a A3 flattop 20-24" stainlees barrel upper.(i think i said that right?)   i really want to reach out and touch something!!!!  i thought i saw a post  about it in here but cannot find it.    please help!

There is no diffrence between lowers that are marked 5.56mm and .223.
The diffrence is when the barrels are marked, .223 can be fired in a barrel marked 5.56mm.
You should not fire 5.56mm in a .223 barrel.
This is because of the diffrence in pressures and chamber design.

THANKS GUYS!!!!!