I have fired an automatic rifle. The noise was astonishingly loud. I'm pretty sure I would struggle to function in that environment. I'd be ok in a war in a library maybe ;)

The SAS training reality series I watched was fascinating. They are looking for control rather than just aggression. The ability to continue to function when under severe pressure and fatigue and stress. The trainees (civvies not military) we
re all super fit. Half of them dropped out in a few days.