After many hours of getting headshots I have found the best sniper class.
SV98: 12x Ballistic Scope & bipod
High-Cap. single shot pistol such as, G17 or MP443
Well that's it and no I did not put the straight bolt on there for a reason. Trust me though I know what I'm talking about I've gotten a 16 killstreak with this and I usually get at least a 10 killstreak.