“Fire with Fire” dark ops help

I have been trying to complete the Fire with Fire dark ops challenge (Kill someone using a Purifier with a Molotov) but I have been struggling like crazy. The Molotov is complete garbage. Any changes to my class setup or any other mode I should play? I have been playing Nuketown for a week and I’m sick of the Crossbar Hades/FMJ 2 Cordite/VMP with constant threshers and gunships.