After Col O'Neill gets shot, he applies a dressing to the outside of his black outer jacket when he should have put it on his skin to stop the bleeding.
Semi-automatic weapons cannot simply fire blanks without modification. They need blank-firing adapters to create the back pressure to push the breech block to the rear, allowing another round to be chambered. Military blank-firing adapters fit into the muzzle and are brightly colored so that everybody involved in an exercise can see the weapon is incapable of firing live rounds. It is theoretically possible that the weapons used in the exercise had "Hollywood adapters" which are not visible, but a quick check of the ammunition in the magazine, which any military trained person would do on receiving a weapon, would reveal blank cartridges.
The guard that gets shot needed to reload his Beretta as the slide was locked in the empty position.