That is what boggles me. Not American, but in Canada we have a tomb of the unknown soldier too, with a permanent posting. Years ago a terrorist killed one of the Guards (RIP Cpl Cirillo) and in response the memorial now has 2 police officers posted to guard the guards..... At a cost of some decent money... Just load their mags! They're their own issued firearms too! Perfectly functioning. And 8760 hours of police officer guard is very expensive per year, a lot more than 30 rounds of 5.56 * 2

Your comment made me want to look it up

Turns out the USA appears keep them loaded, or in their words, "fully functioning"

https://tombguard.org/society/faq/