Reminds me of the old M16-A1. You know - before they had the built-in brass deflector. You could always tell the left handed shooters who didn't button that top button by the three inch burn on their neck.
Had a 30-06 round go down an unbuttoned shirt while shooting National Match High Power Rifle. Not pleasant at all. Still have a scar from that blister. I make sure my shirt is buttoned up completely now whenever shooting.