This guy was instant killing me, a few others were reporting this too. Didn't get any video, and his reports don't conclusively show this, however on his MG4 stats, he has 36277 shots with 633 kills, with an accuracy of 2.08%. Doesn't that mean he only has 755 hits with the MG4? If so (and I've missed something) then that supports what I've experienced in-game.
Thanks