I have a 223 rem bolt carrier assembly, and I put it in a mil spec 5.56 Yankee Hill Upper reciever, or should I go with mil spec 5.56 bolt carrier assembly? This is my first AR build, and I'm scared of doing something wrong here. I finished the gun myself from scratch, but I havent shot it yet. I stayed with 223 ammo just to be sure. Is it safe to shoot 5.56 in the 223 bolt assem, and if I did put the 5.56 bolt I guess itd be fine to shoot 223 in it? Thank You Guys, Yall are always a great help to us newbies.