Interesting thing: for ceremonial rifle inspections, they do seem to be looking down the bore. Of course, all the rifles are cleared and there's no live ammo or mags/clips in (as far as I can tell...) but I guess that just means that's the way they've done it for decades?
Example of it at around 0:45 of this vid of the Arlington Tomb of the Unknown Soldier Changing of the Guard:
https://www.youtube.com/watch?v=iPgFwrxf9N4