Take a look and see what the best sniper rifles are in Call of Duty Black Ops IIII.
Paladin HB50: With 140 base damage and 150 plus head damage this gun is a monster in the right hands. Only two body shots to kill and it is instant death with a headshot. It can be a little slow on the reload, but if you hit a headshot that does not matter.
Outlaw: Now some would say the Paladin is the way to go, but if you look at the stats of the Outlaw. It has 150 plus head damage and is an instant kill with a headshot. However, it has less body damage at 110. The reload rate though is quicker so death by two body shots is actually considerably quicker with this gun. But if you are a sniper, you are playing for the headshot so does it really matter?
SDM: You might have expected me to put the Koska here as it is an instant kill with a headshot, but I think the SDM is the better weapon for a sniper. I say that because while it is a two hit kill for a headshot the kill time for body shots is only 0.42 so if you like playing as a sniper, but cannot always get the headshot, this could be the gun for you.