Cant get "fire kills"

[SwearTaGawd]

Hey guys,

Im struggling to get "fire kills", I have to get 5 per match for 10 matches but have tried everything and nothing seems to count as a "fire kill". I just did 20 molotov cocktail kills in hardcore domination and nada. Used incendiary bullets both direct kills and letting them die from damage over time fire kills and nada. Any suggestions? Thanks!

 

[freakdaddy64]

on the maps theres a boxthat has a bic lighter and a firecracker in it, once you find it you have to run up behind them a hit melee and it sticks it up their butt and they explode.