it all depends on the security nature at the time I can only speak of when I was serving in the British army at the time but on home soil at low threat you had your rifle with empty magazine, next step was rifle and loaded magazine, the next step was rifle loaded magazine and a round chambered. this may have changed and I cant speak for the Americans but that what I was taught. Also if they are doing a gun salute then of course the weapon is loaded but only with blanks other wise you would have some poor sod a few miles away drop down dead.