My cousin is in the army, and he said how unrealistic the grenade launchers are, if it hit you in the chest, it would rip a hole the size of your head out, that's how powerful they are, It hit one of his friends in the hand, it tore most of his hand off, his hand looks a bit like this now (this isnt the actual picture, it's just roughly what it looks like) :
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So yeah it's unrealistic if it hit you in the foot, but if it hit you anywhere other than below your knee and below your shoulder (any part of your arm) you would have an instant death, or you would bleed to death quite quickly.