It's no impossible, I just finished the triumph part today. I ran Blast Furnace + Fighting Lion + Edge Transit.
BF was my main defense weapon whilst I camped near heavy, ET was my preferred GL for getting the doubles/triples and FL was to try and pick the last kill for calculated medals if I only got 2 with the heavy
I put my setup on my Hunter if you want to check it out.
What GL are you trying to use? Fighting Lion? A heavy GL with proximity and blast radius MW really helps, the Play of the Game you get from collections is pretty good as well, you don't want a bouncing grenade.