If it was a "clean-hit", you'd know if you hit your target as the target would drop like a sack of potatoes, as Mudra said, haha!
And yes, have some blood (or even fabric) getting spewed from the back (exit-hole of the bullet) would be ideal, as e.g a 7.76 bullet travelling at reasonable speeds, would really tear you a new butthole (sorry for the mental image I just sent you, haha!).
I'd picture something like this; if you get shot in the chest for instance, you'd be dead/severally injured and you'll fall to the ground in an instance, already dead or being struck by massive hemorrages which will kill you within a few minutes if your heart haven't fried you already. If you get hit in the leg for instance, you'll loose balance and would be impaired/slowed for the first few seconds before you'd potentially loose any reasonable ability to walk - a bullet to the leg isn't anything major in modern times, but with the WW2-caliber rifles/machineguns and few options to stop any bleeding, you'd potentially fracture an arterie/vein and would loose some blood which will further impair your ability to effectivly do some "war-ing".
So to sum it up; chest-shot = dead, or dead within a short timeframe, leg-shot = impaired walking, potentially deadly if a major blood-vessel is struck, but to keep it fair for the gameplay I'd say you'd survive a leg-shot.
Then we could talk some more advanced features like how confusion, stress, hunger, fear etc. would affect your injuries, because they will (!)
Maniche