Hello. Recently I have met this guy. His gameplay has seemed very suspicious. Just look at a profile:
SG510: 447/1079 hs/k (41%)
T45: 170/398 hs/k (43%)
MP7: 83/211 hs/k (39%) and other weapons (except sniper rifles and DMR's)
Believe my experience, it can't be.
Also look at his BF3 statistics:
RPK-74: 39/54 hs/k (72%)
M249: 28/38 hs/k (74%)