Not sure if this is the right place to ask this question but here goes. Can anyone explain the differences between a 5.56 and a .223 and address any safety issues or function problems when shooting them from from either rifle chamberings? I thought they were the same with the only difference being a military designation being used for the 5.56 relative to NATO ammunition markings and use. However, I have heard that rifles chambered 5.56 can shoot a .223 as well. But, a .223 can not handle a 5.56.