That displays a concern for the troops that would be under the flight of the bullets during the exercise. In the CF we held a Crack-Thump training exercise where we were taught to gauge the distance of the incoming fire from a regular, run of the mill C6 (FN MAG) that was pulled out of the armoury with no concern for gauging. It was placed on a berm and held in place by sandbags while we retrieved a 'casualty' who wandered into a minefield, Sketchy as heck in my opinion but we all survived.