I think the military brass is a little thicker and may cause pressure problems. The 5.56 is loaded to higher pressures than the 223. The chamber specifications call for a greater distance between the chamber mouth and the point at which the bullet engages the rifling(called leade)in the military version than the .223. Since one principle of reloading for accuracy calls for the bullet to be seated out to barely touch the rifling, this may cause accuracy problems where there is a large gap. Present day makers of AR15 and Mini14 rifles try to engineer them to handle both types of ammunition. Don't know how effective that is. For your civilian .223 rifle, I would ask the manufacturer for advice on ammunition.I just reload my 223 ammunition using civilian brass and hopefull avoid problems.