I just did a search and came up with this about the weapons of the guards...
"Over the years there have been several different types of weapons used by the Tomb Guards. The changes in weapons reflect the changes in the Army, including M1903 Springfield rifle, M1 Garand and M14 rifles, M1911 .45 ACP and M9 9mm Beretta pistols. Tomb Guards currently carry M14 rifles, which are unloaded, but kept ready for use at all times,
and always have a bayonet fixed."
.......so I presume they carry live ammo....just not loaded live ammo. But then.. he probably only needs the bayonet to get his way..