"Kill trading" in Battlefield 4's PC version is among the glitches fixed in the latest patch DICE rolled out earlier today. A sound-loop bug that had been bothering a lot of people also should be cleared up, too. Many more details are here.
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i don't know how to feel about "kill trading", in real life, the fact that you kill an enemy first, doesn't make their bullets dissapear, i know is very annoying on video games though