If you've looked at how a lot of soldiers' rifles are slung these days when on patrol, they beat a soldiers legs pretty good unless his has a hand on the weapon to steady it.
Been there....carried one. Unless the rifle is slung tight across the back, one simply cannot let it drop and swing freely when 2 hands are needed for other things.
Hmmm ... yes, I see what you mean. That rifle down at waist level must beat your thighs up a bit. If she's shorter than she looks, maybe even more than "a bit".