When firing in third person -- mini gun, g36, carbine (and probably more) -- there is a bug where your own bullets hit your avatar and never travel to the enemy.
To recreate the bug, be in third-person view while aiming down sights (minigun easiest to replicate) and fire while strafing right in the crouched position. Strafing to the left can also create this bug, but right is easiest to replicate. Blood splatter and hit noise will occur on your own character, but you take no damage.