Tim explains it well over at Gun Nuts.
Tim and I were in a class together recently where we ran into a similar issue. Another instructor teaching on the bay next to ours thought it was perfectly safe to have his carbine students climb up a hill behind us and shoot… from a position in clear line of sight to everyone on our bay.
In other words, if any of them had moved his muzzle about two inches to the right — even accidentally — their rounds would have been flying through the same three dimensional space being occupied by our heads. The worst part is that their instructor was dumbfounded by our concern and it took more than a polite request to get him to call a halt to their plan. Here’s a guy who is claiming to teach high speed cool guy combat carbinery and he doesn’t understand that maybe some of his novice students could, you know, make a mistake. As one of the guys from our class noted, quite a few of the carbine students themselves looked pretty uncomfortable with what they were being asked to do.
Is muzzle safety really so complicated?
Train hard & stay safe! ToddG