Used damage modifiers to increase his damage per shot. Kills almost instantly. 
http://battlelog.battlefield.com/bf4/battlereport/show/1/878603728036384960/214063278/
In the battlereport, the round lasted 34 minutes during which he was able to get 156 Kills. That's a KPM of 4.58. He got a 45 killstreak just 5 minutes after he joined the server. Always one shot killing.

http://bf4db.com/player/214063278/snapshot/2300