I am pretty sure this guy is cheating, i played against him and he killed way too quik with lmg so i started to check his stats, his accuracy is wildly inconsistent, from up to 38% to as low as 4% .. also rejoining just before end of round is very typical behaviour , all in all im fairly sure this is not legit .

to me this looks like without 3rd party software : http://battlelog.battlefield.com/bf4/battlereport/show/1/882185812313556608/1049759058/

this looks like with 3rd party software: http://battlelog.battlefield.com/bf4/battlereport/show/1/882207516183869248/1049759058/

I came across him too. Definitely cheating.

Locker. 62 kills 46 headshots with LMG :

http://battlelog.battlefield.com/bf4/battlereport/show/1/882582039995955328/1049759058/

Locker. Here it's the opposite. 57 kills 3 headshots, LMG too :

http://battlelog.battlefield.com/bf4/battlereport/show/1/882582039995955328/1049759058/

AKU-12 : 157 kills 35% accuracy, and only 5 headshots.