I'm after a type of gun. I want it to be an automatic weapon that's good enough to be used as a sniper rifle ( at short range, about two/three stories up directly across the street from the target) by someone who is a very good shot. I'd really like it to be a gun that's identifiable to those under fire by the sound it makes and common enough that it wouldn't have to be the shooters own weapon, he can leave it at the scene. I also want the shooter to be using a bullet that will pass through without doing vast amounts of damage. I.E. a headshot will leave the head intact, a bodyshot won't make massive holes in the torso.
I'm clueless about weapons. Can anyone help me out?
***Edit** It would be enough just to know from the sound it's a rifle of some sort not a handgun. Can anyone tell me the difference in sound?
**Edit2** And I've worked around the damage, it can do lots of damage I have a way out. And I'd quite like to use the words "High velocity Spatter" too.