If you want "Unyielding
" easy and not have to worry about A.I., set up a Team game (one with unlimited respawns, like Team Elimination: Sharpshooter) with a second controller. Spawn kill the second controller 30 times... unlocked. Set the time for 30 minutes. They spawn in one of three locations. You can cover two of them from the same spot.
Here is probably the best solution for "Heavyweight
". Found this on TA.