@Alligatorob
Real or "live" ammunition should NEVER be present on set, as has been stated by several professional armorers in some of the articled linked above. No exceptions.
@rgp
I've seen those reports also. If true, that would be a major breakdown of safety rules. Again, there should never be live ammunition anywhere on or near the set, and the prop master or armorer should always be present and in personal control of his guns.
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"Blanks" are easy to identify because there is no bullet in cartridge case. Either the end of the case is crimped or there is some "wadding" (typically paper) where the bullet would be. These are obviously not live rounds.
In addition to blanks, there are also various types of "dummy" rounds which look exactly like live rounds, but contain no gunpowder and no primer charge. Most such center fire rounds I've seen had either a used, "dimpled" primer or no primer at all, and rimfire rounds had the usual mark on the edge. These are easy to identify, and are (or should be) used whenever the audience can see the cartridges, but not closely enough to see if the primer is missing or dimpled. For example cartridge belts or western gun belts.
But there are also dummy rounds which really do look exactly like live rounds. These are used when the audience will see the cartridges up close, such as when a gun is being loaded in the scene, or the characters are handling ammunition for some reason. Live ammo should never be on set because if it's not there, it can't get confused with props, can't get into a gun, and can't kill anyone.