I don't have a video but if someone would like to make one more power to ya.
When an enemy soldier gets on a mounted machine gun, aim under his head there should be the ammo drum of the weapon. Using zoom/bullet time you should be able to ricochet a shot up into his head (neck counts as head-shot) I got it on the first mission after the prologue (SCHONEBERG CONVOY) there's a MG placement in the building above and left of where you take out the enemy patrols.
